ffprobe: restore reporting error code for failed inputs

c11fb46731 led to a regression whereby the return code for missing
input or input probe is overridden by writer close return code and
hence not conveyed in the exit code.

fftools/ffprobe.c

@@ -4032,7 +4032,7 @@ int main(int argc, char **argv)
     WriterContext *wctx;
     char *buf;
     char *w_name = NULL, *w_args = NULL;
-    int ret, i;
+    int ret, input_ret, i;
 
     init_dynload();
 
@@ -4156,10 +4156,14 @@ int main(int argc, char **argv)
                 show_error(wctx, ret);
         }
 
+        input_ret = ret;
+
         writer_print_section_footer(wctx);
         ret = writer_close(&wctx);
         if (ret < 0)
             av_log(NULL, AV_LOG_ERROR, "Writing output failed: %s\n", av_err2str(ret));
+
+        ret = FFMIN(ret, input_ret);
     }
 
 end: