ffools/ffmpeg_filter: stop trying to handle an unreachable state

ifilter_send_eof() will fail if the input has no real or fallback
parameters, so there is no need to handle the case of some inputs being
in EOF state yet having no parameters.

fftools/ffmpeg_filter.c

@@ -2081,11 +2081,11 @@ int fg_transcode_step(FilterGraph *graph, InputStream **best_ist)
             }
         }
 
-        // graph not configured, but all inputs are either initialized or EOF
-        for (int i = 0; i < graph->nb_outputs; i++)
-            graph->outputs[i]->ost->inputs_done = 1;
-
-        return 0;
+        // This state - graph is not configured, but all inputs are either
+        // initialized or EOF - should be unreachable because sending EOF to a
+        // filter without even a fallback format should fail
+        av_assert0(0);
+        return AVERROR_BUG;
     }
 
     *best_ist = NULL;