Fix a crash in Canvas.drawBitmap if empty dest rect is passed

Fix a crash in Canvas.drawBitmap if an empty dest or source rect
is passed. This issue is specific to Skia pipeline only.

Test: Ran hwui unit tests and verified nexuslauncher is not
crashing anymore.

Change-Id: I3f9f96d03541e960d463836200d2b01269b5e008