This reverts basically the changes from my last commit #362 except that the exception, that was causing crashes reported in #361 and #287 is caught an a fall back is provided. Personally I am not really sure if we should merge this, because this code assumes what is before and after the dash in the custom date format (that was already the case before my commit #362), but if you want to you can use all kinds of wonky stuff as custom date format (e.g. " - HH:mm" won't show any date in the widget [I know, nobody would use this format, I am just pointing out the flaws of this code]). But at least the crahses should be fixed and all the predefined formats work again for the widget.

Fixing crashes is a good thing, so I'm prepared to accept this pull. Could you take a look at this PR, let me know if there's any problems in accepting it also? #326