showfiltfmts: destroy filter context before exit

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@24722 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

tools/lavfi-showfiltfmts.c

@@ -93,6 +93,7 @@ int main(int argc, char **argv)
                    av_pix_fmt_descriptors[fmts->formats[j]].name);
     }
 
+    avfilter_destroy(filter_ctx);
     fflush(stdout);
     return 0;
 }