Fixed incorrect calculation of dirty invalidation area

Padding was already taken into consideration before calling
invalidateDrawable in ProgressBar.

Change-Id: I75f25b0b7ee87d394422c58888ed3a1cca5d06a8
Fix error checking in MemoryFile.

mmap returns MAP_FAILED on failures, not 0 (NULL).
Also, convert some C style casts to C++ since they
make intent clearer.

Change-Id: I367993c73e9ee576f11ebe76e530d2c2f27c662d