Fix for wrong alignment using texture format sizes other than 4 bytes.
For example RGBA4444 is 2 bytes per pixel. A texture with width of 1 passes the previous power of 2 test, but the alignment value needs to be 2, not 4.
Merge pull request #2551 from silverscania/master

Fix for corrupted texture issue: https://github.com/cocos2d/cocos2d-x/issues/2550