Fix issue 82 Gallery crashes if it has only one tab

[bigMOTOR]

STR:

• set Config.tabsToShow = [.imageTab] (one tab only);
• run app.

Result: Crash with "Fatal error: Unexpectedly found nil while unwrapping an Optional value" in line 97 of PagesController class.

[3lvis]

Hi @bigMotor, sorry for the lack of follow up, Gallery was entered into maintenance mode and didn't have someone following up issues. Since it's been a while since you submitted this I'm wondering if it's still relevant.

Thanks for your time and have a nice week.