Avert crash when dragging text in same TextView

The previous implementation made liberal assumptions about the size
of the string being edited, as well as the position of the substring
being dragged. Explicitly checking those assumptions fixes our
IndexOutOfBoundsException.

Bug: 7129392
Change-Id: I32560cf87fbbe703a8b26c7eb2a64c8f8c0bfcf1
1 file changed