Bug 816260 - Hotspot Settings: No error message is displayed when Wi-Fi hotspot SSID is blank r='kaze'

An error Alert message is displayed in case of empty SSID and the fields are reverted to previous settings.
Merge pull request #8280 from MrDHat/Bug-816260

Bug 816260 - Hotspot Settings: No error message is displayed when Wi-Fi hotspot SSID is blank, r=kaze