Fix in nested block handling. @maydiscard and @nodiscard annotations. If the common type of int[x] and int[y] is int[]

lib/std/core/string.c3

@@ -196,7 +196,7 @@ fn void String.destroy(String* str)
 	if (!*str) return;
 	StringData* data = str.data();
 	if (!data) return;
-	data.allocator.free(data);
+	data.allocator.free(data)!!;
 	*str = (String)null;
 }