VideoCommon: return 0 if bbox is disabled

Through just returning the last written value sounds better, this crashes Paper Mario.
In my opinion, gfx issues are fine on older GPUs, but crashes should not happen.

Source/Core/VideoCommon/MainBase.cpp

@@ -153,7 +153,7 @@ u32 VideoBackendHardware::Video_GetQueryResult(PerfQueryType type)
 u16 VideoBackendHardware::Video_GetBoundingBox(int index)
 {
 	if (!g_ActiveConfig.backend_info.bSupportsBBox || !g_ActiveConfig.bBBoxEnable)
-		return BoundingBox::coords[index];
+		return 0;
 
 	SyncGPU(SYNC_GPU_BBOX);