Fix the crash issue for debug version when restoring texture binding at Unit 0 in DrawingBuffer::prepareMailbox()

BUG=254345

Review URL: https://chromiumcodereview.appspot.com/17835002

git-svn-id: svn://svn.chromium.org/blink/trunk@153065 bbb929c8-8fbe-4397-9dbb-9b2b20218538
1 file changed