surfaceflinger: don't check HWComposer numLayers unless one exists
surfaceflinger: don't check HWComposer numLayers unless one exists

Change-Id: I4b83f7bf7ba1318c70054117f14e759fe0ad105c

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