jimp: fix compilation on clang

jimp.h

@@ -237,10 +237,11 @@ static bool jimp__get_token(Jimp *jimp)
                 jimp->token = JIMP_STRING;
                 return true;
             }
-            default:
+            default: {
                 char x = *jimp->point++;
                 jimp__append_to_string(jimp, x);
             }
+            }
         }
         jimp->token = JIMP_INVALID;
         jimp_diagf(jimp, "ERROR: unfinished string\n");