Fixed bug in BitmapFactory.decodeStream

Downloading images over a slow connection could result in errors and
null images.

The JavaInputStreamAdaptor::do_skip method was correctly called in a
loop (to handle the EOF case using read()), but the amount that was
skipped at each time was not decreased by the amount already skipped.

Bug http://code.google.com/p/android/issues/detail?id=6066

Cherry picked from master CL57808

Change-Id: Ie6856898b21ba31de1209e1f995b4ae784c919b9