If imageSize is 0, inputPitch may be 0, which would cause a division
by 0. In any case, if imageSize is 0, there's no work to perform, so
we just skip loadCompressedData() entirely in that case.

Bug:765094

Change-Id: Iedc6516ef6d025d24a8827597045cb3b83599e4a
Reviewed-on: https://swiftshader-review.googlesource.com/12648Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>