fftools/ffmpeg_filter: try configuring graphs from input EOF

When a filtergraph input receives EOF but never saw any input frames, we
use the fallback parameters. Currently an attempt to actually configure
the filtergraph will happen elsewhere, but there is no reason to
postpone this.

fftools/ffmpeg_filter.c

@@ -1533,6 +1533,14 @@ int ifilter_send_eof(InputFilter *ifilter, int64_t pts, AVRational tb)
                                          &ifp->fallback.ch_layout);
             if (ret < 0)
                 return ret;
+
+            if (ifilter_has_all_input_formats(ifilter->graph)) {
+                ret = configure_filtergraph(ifilter->graph);
+                if (ret < 0) {
+                    av_log(NULL, AV_LOG_ERROR, "Error initializing filters!\n");
+                    return ret;
+                }
+            }
         }
 
         if (ifilter->format < 0 && (ifilter->type == AVMEDIA_TYPE_AUDIO || ifilter->type == AVMEDIA_TYPE_VIDEO)) {