Prevent unhandled exception in NinePatchDrawable

Added null check in computeBitmapSize() to avoid unhandled
exception "java.lang.NullPointerException" at
android.graphics.Rect.<init>(Rect.java:72).

This problem was discovered in the wild.

Change-Id: I9d40629a052f1390e1811288af6209d8cc3f679b
1 file changed