avfilter/vf_signature: Fix leak of inpads' names

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 37838417b8)

libavfilter/vf_signature.c

@@ -731,6 +731,8 @@ static av_cold void uninit(AVFilterContext *ctx)
         }
         av_freep(&sic->streamcontexts);
     }
+    for (unsigned i = 0; i < ctx->nb_inputs; i++)
+        av_freep(&ctx->input_pads[i].name);
 }
 
 static int config_output(AVFilterLink *outlink)