fix broken comparisons

These are fixes for three broken comparisons taken from https://github.com/notspiff/xbmc-cmake/commit/f66398523382bae1d6c46eafba2a8e738a3f57fe (thanks @notspiff). I didn't cherry-pick the original commit because I've stopped an additional simplification/optimization in it.

They might be harmless enough for 13.x.