Bilinear interpolation doesn't work with StackedAreaDefinitions

[pnuu]

Describe the bug
Bilinear interpolation doesn't work when the area of the input data is StackedAreaDefinition. An example of this case is MSG/SEVIRI with a missing segment from the middle of the disk, or the HRV channel when there are segments available for both of the imaging windows.

To Reproduce

import glob
from satpy import Scene

fnames = glob.glob("H*__")
glbl = Scene(reader='seviri_l1b_hrit', filenames=fnames)
glbl.load(['HRV'])
lcl = glbl.resample('euro4', resampler='bilinear')
lcl.save_datasets(base_dir='/tmp')

Expected behavior
Image of HRV channel resampled to euro4 area.

Actual results
Empty image of euro4 area.

Environment Info:

• Any recent (xarray/dask based) Satpy
• PyResample Version: 0.12.0 (also earlier versions seem to have the same issue)