Fix for an IOOBoundsException in Paint.

Bug 3331706

The temporary buffer starts at index 0 and shifts indexes by contextStart.
offset has to be changed accordingly.

Note that I didn't try to reproduce the monkey bug after this fix, but it
seems like a perfect explanation for the exception.

Change-Id: Ie69adc413670caed283bc46effc69f17a102922c
1 file changed