mesa: avoid leaking closure when iterating over a string_to_uint_map

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>

src/mesa/program/hash_table.h

@@ -249,6 +249,7 @@ public:
       wrapper->closure = closure;
 
       hash_table_call_foreach(this->ht, subtract_one_wrapper, wrapper);
+      free(wrapper);
    }
 
    /**