Fix rescale using small scale factor

[rfezzani]

Description

Fixes #5252.

The proposed fix is to return a 1 pixel image when a very small scale factor is used for rescaling an image:

>>> img = zeros((2, 2))
>>> out = rescale(img, 0.1)  # current behavior is to raise an error as reported in #5252
>>> print(out)  # with this PR
[[0.]]

An other option would be to raise a proper error message instead of the actual OverflowError. What do you, reviewers, prefer?

Checklist

• Docstrings for all functions
• Gallery example in ./doc/examples (new features only)
• Benchmark in ./benchmarks, if your changes aren't covered by an
  existing benchmark
• Unit tests
• Clean style in the spirit of PEP8

For reviewers

• Check that the PR title is short, concise, and will make sense 1 year
  later.
• Check that new functions are imported in corresponding __init__.py.
• Check that new features, API changes, and deprecations are mentioned in
  doc/release/release_dev.rst.

[jni]

neat! 😊