options.c: Move hold-action check to check_options.

In feh_parse_option_array, when a hold-action is set from a theme it would
behave differently than one set from commandline.

Theme: ;;foo would become foo (incorrect)
cmdline: ;;foo would become ;foo (correct)

I doubt anybody would ever have noticed it, since ;foo is a shell syntax error
anyways, but it's definitely better to be on the safe side.