Adjust a fucntion signature

ext/zlib/zlib.c

@@ -4277,13 +4277,19 @@ rb_gzreader_external_encoding(VALUE self)
 }
 
 static VALUE
-zlib_gzip_ensure(VALUE arg)
+zlib_gzip_end_rescue(VALUE arg)
 {
     struct gzfile *gz = (struct gzfile *)arg;
-    rb_rescue((VALUE(*)())gz->end, arg, NULL, Qnil);
+    gz->end(gz);
     return Qnil;
 }
 
+static VALUE
+zlib_gzip_ensure(VALUE arg)
+{
+    return rb_rescue(zlib_gzip_end_rescue, arg, NULL, Qnil);
+}
+
 static void
 zlib_gzip_end(struct gzfile *gz)
 {