Merge commit 'b8cd7a3c'

* commit 'b8cd7a3c':
  dvbsub: Check for errors from system()

printf(...) replaced with fprintf(stderr, ...) for logging errors.
Merged-by: Clément Bœsch <u@pkh.me>

libavcodec/dvbsubdec.c

@@ -85,10 +85,16 @@ static void png_save(const char *filename, uint32_t *bitmap, int w, int h)
     fclose(f);
 
     snprintf(command, sizeof(command), "pnmtopng -alpha %s %s > %s.png 2> /dev/null", fname2, fname, filename);
-    system(command);
+    if (system(command) != 0) {
+        fprintf(stderr, "Error running pnmtopng\n");
+        return;
+    }
 
     snprintf(command, sizeof(command), "rm %s %s", fname, fname2);
-    system(command);
+    if (system(command) != 0) {
+        fprintf(stderr, "Error removing %s and %s\n", fname, fname2);
+        return;
+    }
 }
 #endif