Adding test case to verify #248 - zero password login

This test verifies that it is possible to exploit the authentication adapter of DoctrineModule to
login into a system if the password is zero, empty or casted to zero.
Applying fix for #248

As suggested by @bakura10, this fix removes the security hole by preventing automatic type casting from affecting authentication via zero password
Merge branch 'hotfix/issue-#248-zero-password-login' - fixes #248 - diallows zero-password-login