fix a crasher in surfaceflinger
fix a crasher in surfaceflinger

this would happen if being told to draw before a buffer
was available.

Change-Id: I46d121c73e883078cdbf952063e38b0076f79038

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base