id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
710876876,MDU6SXNzdWU3MTA4NzY4NzY=,4471,"Numeric scalar variable attributes (including fill_value, scale_factor, add_offset) are 1-d instead of 0-d with h5netcdf engine, triggering ValueError: non-broadcastable output on application when loading single elements",500246,closed,0,,,13,2020-09-29T08:15:48Z,2020-10-11T20:06:33Z,2020-10-11T20:06:33Z,CONTRIBUTOR,,,,"<!-- Please include a self-contained copy-pastable example that generates the issue if possible.

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**What happened**:

When I try to open a NetCDF file using the `h5netcdf` engine, accessing a single data point before scale factors have been applied results in `ValueError: non-broadcastable output operand with shape () doesn't match the broadcast shape (1,)`.  The MCVE (see below) results in:

```
Traceback (most recent call last):
  File ""mwe93.py"", line 4, in <module>
    ds[""Rad""][400, 300].load()
  File ""/data/gholl/miniconda3/envs/py38b/lib/python3.8/site-packages/xarray/core/dataarray.py"", line 808, in load
    ds = self._to_temp_dataset().load(**kwargs)
  File ""/data/gholl/miniconda3/envs/py38b/lib/python3.8/site-packages/xarray/core/dataset.py"", line 662, in load
    v.load()
  File ""/data/gholl/miniconda3/envs/py38b/lib/python3.8/site-packages/xarray/core/variable.py"", line 439, in load
    self._data = np.asarray(self._data)
  File ""/data/gholl/miniconda3/envs/py38b/lib/python3.8/site-packages/numpy/core/_asarray.py"", line 83, in asarray
    return array(a, dtype, copy=False, order=order)
  File ""/data/gholl/miniconda3/envs/py38b/lib/python3.8/site-packages/xarray/core/indexing.py"", line 685, in __array__
    self._ensure_cached()
  File ""/data/gholl/miniconda3/envs/py38b/lib/python3.8/site-packages/xarray/core/indexing.py"", line 682, in _ensure_cached
    self.array = NumpyIndexingAdapter(np.asarray(self.array))
  File ""/data/gholl/miniconda3/envs/py38b/lib/python3.8/site-packages/numpy/core/_asarray.py"", line 83, in asarray
    return array(a, dtype, copy=False, order=order)
  File ""/data/gholl/miniconda3/envs/py38b/lib/python3.8/site-packages/xarray/core/indexing.py"", line 655, in __array__
    return np.asarray(self.array, dtype=dtype)
  File ""/data/gholl/miniconda3/envs/py38b/lib/python3.8/site-packages/numpy/core/_asarray.py"", line 83, in asarray
    return array(a, dtype, copy=False, order=order)
  File ""/data/gholl/miniconda3/envs/py38b/lib/python3.8/site-packages/xarray/core/indexing.py"", line 560, in __array__
    return np.asarray(array[self.key], dtype=None)
  File ""/data/gholl/miniconda3/envs/py38b/lib/python3.8/site-packages/numpy/core/_asarray.py"", line 83, in asarray
    return array(a, dtype, copy=False, order=order)
  File ""/data/gholl/miniconda3/envs/py38b/lib/python3.8/site-packages/xarray/coding/variables.py"", line 70, in __array__
    return self.func(self.array)
  File ""/data/gholl/miniconda3/envs/py38b/lib/python3.8/site-packages/xarray/coding/variables.py"", line 220, in _scale_offset_decoding
    data *= scale_factor
ValueError: non-broadcastable output operand with shape () doesn't match the broadcast shape (1,)
```


**What you expected to happen**:

I expect the data access to work similarly as when opening with other engines.

**Minimal Complete Verifiable Example**:

```python
import xarray
fn = ""/data/gholl/cache/fogtools/abi/2017/03/14/20/06/7/OR_ABI-L1b-RadF-M3C07_G16_s20170732006100_e20170732016478_c20170732016514.nc""
with xarray.open_dataset(fn, engine=""h5netcdf"") as ds:
    ds[""Rad""][400, 300].load()
```

**Anything else we need to know?**:

An earlier version of this issue, and some comments, refer to fsspec or working on open files, but that proved to have nothing to do with the problem.  

**Environment**:

I've confirmed this issue installing xarray from latest master, which means xarray 0.16.2.dev11+gf821fe20 at the time of writing,

<details><summary>Output of <tt>xr.show_versions()</tt></summary>


INSTALLED VERSIONS
------------------
commit: None
python: 3.8.5 | packaged by conda-forge | (default, Sep 24 2020, 16:55:52) 
[GCC 7.5.0]
python-bits: 64
OS: Linux
OS-release: 4.12.14-lp150.12.82-default
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: en_GB.UTF-8
libhdf5: 1.10.6
libnetcdf: 4.7.4

xarray: 0.16.2.dev11+gf821fe20
pandas: 1.1.2
numpy: 1.19.1
scipy: 1.5.2
netCDF4: 1.5.4
pydap: None
h5netcdf: 0.8.1
h5py: 2.10.0
Nio: None
zarr: 2.4.0
cftime: 1.2.1
nc_time_axis: None
PseudoNetCDF: None
rasterio: 1.1.6
cfgrib: None
iris: None
bottleneck: None
dask: 2.27.0
distributed: 2.27.0
matplotlib: 3.3.2
cartopy: None
seaborn: None
numbagg: None
pint: None
setuptools: 49.6.0.post20200917
pip: 20.2.3
conda: None
pytest: 6.0.2
IPython: None
sphinx: None

</details>
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