Fixed validation errors not showing after failed save in editor
Fixed validation errors not showing after failed save in editor

refs https://github.com/TryGhost/Admin/commit/a6c6def7e18548409967f4d873fbfcf36f07cc5f

- we weren't checking if an error was a validation error by examining the number of errors on the post model, this meant we weren't falling through to the generic error handling/display logic that shows an alert for validation errors when a save isn't a background/silent save

TryGhost/Ghost,TryGhost/Ghost,TryGhost/Ghost