[Validator] Test that validateProperty() works if no constraint is defined

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes (2.3 has to be merged into 2.5 first)
| Fixed tickets | #11604, #11614
| License       | MIT
| Doc PR        | 

Adds a test case for #11604 to avoid regressions. The actual issue has been fixed in Symfony 2.3 with the merge of #11615.