avdevice/dshow: Check ICaptureGraphBuilder2_SetFiltergraph() for failure

Fixes: CID1591939 Logically dead code

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavdevice/dshow.c

@@ -1465,7 +1465,7 @@ dshow_open_device(AVFormatContext *avctx, ICreateDevEnum *devenum,
         av_log(avctx, AV_LOG_ERROR, "Could not create CaptureGraphBuilder2\n");
         goto error;
     }
-    ICaptureGraphBuilder2_SetFiltergraph(graph_builder2, graph);
+    r = ICaptureGraphBuilder2_SetFiltergraph(graph_builder2, graph);
     if (r != S_OK) {
         av_log(avctx, AV_LOG_ERROR, "Could not set graph for CaptureGraphBuilder2\n");
         goto error;