Lack of error handling for invalid parameters on controller actions

[20wildmanj]

The following actions don't have proper error checking if an invalid parameter is provided:

• users/change_password_for_user
• users/update_password_for_user
• users/update_display_settings

Note from Chaskiel:
Note that there should be some better error handling in those methods. Sending a bad user :id results in a form rendering error - there's no nil check for the user lookup in change_password_for_user