desktop-file test: Free result on all code paths

Otherwise, Coverity will diagnose this as a resource leak,
because it doesn't understand that our assertions end up guaranteeing
that the result is freed if and only if it's non-`NULL`.

Coverity CID: 354884

test/internals/desktop-file.c

@@ -221,8 +221,8 @@ test_content (const Test *test,
           test_assert_no_error (&error);
           g_assert_true (ok);
           g_assert_cmpstr (val, ==, test->value);
-          dbus_free (val);
         }
+      dbus_free (val);
     }
 }