[1.1, 1.2, 1.3] sfDoctrineGuardPlugin: Fixes issue with guard signin issues a query even when username is empty (closes #6636)
[1.1, 1.2, 1.3] sfDoctrineGuardPlugin: Fixes issue with guard signin issues a query even when username is empty (closes #6636)


schwarz-computer-systeme/sfDoctrineGuardPlugin,MiLk/sfMangosGuardPlugin