mesa/main/debug: Check if we successfully reopened the ppm file.

Since we created the file, we should be able to reopen it for appending, but
some weird filesystem error could cause that to be false. So simply check
whether we could reopen it or not.

CID: 1177144
Signed-off-by: Rafael Antognolli <rafael.antognolli@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/mesa/main/debug.c

@@ -235,6 +235,11 @@ write_ppm(const char *filename, const GLubyte *buffer, int width, int height,
       fprintf(f,"255\n");
       fclose(f);
       f = fopen( filename, "ab" );  /* reopen in binary append mode */
+      if (!f) {
+         fprintf(stderr, "Error while reopening %s in write_ppm()\n",
+                 filename);
+         return;
+      }
       for (y=0; y < height; y++) {
          for (x = 0; x < width; x++) {
             int yy = invert ? (height - 1 - y) : y;