[Bug] Fix formatting of anonymous labels (#362)

Anonymous labels accidentally called `sb.append` instead of
`sb.appendFormat` which messes up the label's formatting.

src/asmjit/core/formatter.cpp

@@ -143,7 +143,7 @@ Error formatLabel(
     }
 
     if (le->type() == LabelType::kAnonymous)
-      ASMJIT_PROPAGATE(sb.append("L%u@", labelId));
+      ASMJIT_PROPAGATE(sb.appendFormat("L%u@", labelId));
     return sb.append(le->name());
   }
   else {