user32: test what FindWindow when window isn't found

[Juan Lang]

Hi Austin,

+    found = FindWindow("SomeWindowThatDoesNotExist", NULL);
+    if(found) {
+      printf("found not NULL");
+    }

Please don't use printf in the tests.  If you must log something, use
trace, but I don't think it's that useful in this case, since we
really expect it not to be found.
--Juan