opengles emulator: fix the mixing between pack/unpack alignments

The was a bug in the calculation of the pixels data size, caused by wrong usage
of pack/unpack alignment.
Pack should be used for glReadPixels, while unpack should be used for glTexImage and such.
Also fixes crash in "Angry Birds" & "Angry Birds Rio"

Change-Id: I099308a57a1ea907d38c59bad056429bc107de98
2 files changed