ImgIoUtilReadFile: check ftell() return

This avoids attempting to allocate 0 bytes if the call fails. (An
additional byte is added to the result to allow a '\0' to be appended.)

Bug: chromium:334120888
Change-Id: Ifcb8ff7744c567cbd08051aa04cc66acf936078d

imageio/imageio_util.c

@@ -89,6 +89,11 @@ int ImgIoUtilReadFile(const char* const file_name,
   }
   fseek(in, 0, SEEK_END);
   file_size = ftell(in);
+  if (file_size == (size_t)-1) {
+    fclose(in);
+    WFPRINTF(stderr, "error getting size of '%s'\n", (const W_CHAR*)file_name);
+    return 0;
+  }
   fseek(in, 0, SEEK_SET);
   // we allocate one extra byte for the \0 terminator
   file_data = (uint8_t*)WebPMalloc(file_size + 1);