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
1183858748,I_kwDOAMm_X85GkEA8,6424,DataArray.plot.contourf() fails when data has no positive values,42851573,closed,0,,,3,2022-03-28T19:00:33Z,2022-03-30T14:28:51Z,2022-03-30T14:28:51Z,NONE,,,,"### What happened?

For a DataArray with no positive values, the `plot.contourf()` fails to produce the correct figure. It makes the contourf plot and returns successfully, but emits several warnings and does not complete the colorbar. Two sample screenshots are in \<details> below.

The `plot.contour()` function has the same behavior, but only when `add_colorbar=True`.

### What did you expect to happen?

_No response_

### Minimal Complete Verifiable Example

```Python
import xarray as XR
da = xr.DataArray(np.arange(20).reshape(4,5), dims=('x','y'))
da.plot.contourf() # successful (first image below)
(da-19).plot.contourf() # fails (second image below)
```


### Relevant log output

```Python
> da = xr.DataArray(np.arange(20).reshape(4,5), dims=('x','y'))

> da
<xarray.DataArray (x: 4, y: 5)>
array([[ 0,  1,  2,  3,  4],
       [ 5,  6,  7,  8,  9],
       [10, 11, 12, 13, 14],
       [15, 16, 17, 18, 19]])
Dimensions without coordinates: x, y

> da.plot.contourf() # successful (first image below)
<matplotlib.contour.QuadContourSet at 0x299dc2940>

> (da-18).plot.contourf() # successful
<matplotlib.contour.QuadContourSet at 0x299dc2940>

> (da-19).plot.contourf() # fails (second image below)
<matplotlib.contour.QuadContourSet at 0x299dc2940>
~/miniconda3/envs/plots/lib/python3.9/site-packages/matplotlib/transforms.py:2663: RuntimeWarning: divide by zero encountered in double_scalars
  y_scale = 1.0 / inh
~/miniconda3/envs/plots/lib/python3.9/site-packages/matplotlib/transforms.py:2665: RuntimeWarning: invalid value encountered in double_scalars
  [0.0    , y_scale, (-inb*y_scale)],
posx and posy should be finite values
posx and posy should be finite values
posx and posy should be finite values
posx and posy should be finite values

> da-19
<xarray.DataArray (x: 4, y: 5)>
array([[-19, -18, -17, -16, -15],
       [-14, -13, -12, -11, -10],
       [ -9,  -8,  -7,  -6,  -5],
       [ -4,  -3,  -2,  -1,   0]])
Dimensions without coordinates: x, y
```


### Anything else we need to know?

<details><summary>
Screenshots of plots
</summary>

```python
> da.plot.contourf() # successful
```

<img width=""550"" alt=""image"" src=""https://user-images.githubusercontent.com/42851573/160464804-ba38e4a5-ff0f-49c2-ba2a-785856b575d6.png"">

```python
> (da-19).plot.contourf() # fails
```

<img width=""550"" alt=""image"" src=""https://user-images.githubusercontent.com/42851573/160465025-78167983-d0f1-4012-bcd8-bf5271daf9f0.png"">
</details>

### Environment

<details><summary>xr.show_versions()</summary>
miniconda3/envs/plots/lib/python3.9/site-packages/_distutils_hack/__init__.py:30: UserWarning: Setuptools is replacing distutils.
  warnings.warn(""Setuptools is replacing distutils."")

INSTALLED VERSIONS
------------------
commit: None
python: 3.9.12 | packaged by conda-forge | (main, Mar 24 2022, 23:25:14)
[Clang 12.0.1 ]
python-bits: 64
OS: Darwin
OS-release: 21.3.0
machine: arm64
processor: arm
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: ('en_US', 'UTF-8')
libhdf5: 1.12.1
libnetcdf: 4.8.1

xarray: 2022.3.0
pandas: 1.3.5
numpy: 1.21.5
scipy: 1.7.1
netCDF4: 1.5.7
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: 1.6.0
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: 1.3.4
dask: 2022.03.0
distributed: None
matplotlib: 3.5.0
cartopy: 0.20.2
seaborn: None
numbagg: None
fsspec: 2022.02.0
cupy: None
pint: None
sparse: None
setuptools: 61.2.0
pip: 22.0.4
conda: None
pytest: None
IPython: 7.29.0
sphinx: None
</details>","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/6424/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue