Fix memory leak in util_spec_rb_get_kwargs

The call to rb_get_kwargs could raise an exception, which would cause
the ids and results to be leaked. This commit changes these two to be
allocated on the stack using alloca instead of malloc so we don't need
to free it.

optional/capi/ext/util_spec.c

@@ -62,22 +62,17 @@ static VALUE util_spec_rb_get_kwargs(VALUE self, VALUE keyword_hash, VALUE keys,
   int len = RARRAY_LENINT(keys);
 
   int values_len = req + (opt < 0 ? -1 - opt : opt);
-  int i = 0;
 
-  ID *ids = (ID*) malloc(sizeof(VALUE) * len);
-  VALUE *results = (VALUE*) malloc(sizeof(VALUE) * values_len);
-  int extracted = 0;
-  VALUE ary = Qundef;
+  ID *ids = (ID *)alloca(sizeof(VALUE) * len);
+  VALUE *results = (VALUE *)alloca(sizeof(VALUE) * values_len);
 
-  for (i = 0; i < len; i++) {
+  for (int i = 0; i < len; i++) {
     ids[i] = SYM2ID(rb_ary_entry(keys, i));
   }
 
-  extracted = rb_get_kwargs(keyword_hash, ids, req, opt, results);
-  ary = rb_ary_new_from_values(extracted, results);
-  free(results);
-  free(ids);
-  return ary;
+  int extracted = rb_get_kwargs(keyword_hash, ids, req, opt, results);
+
+  return rb_ary_new_from_values(extracted, results);
 }
 
 static VALUE util_spec_rb_long2int(VALUE self, VALUE n) {