recur.c: Refactor/Reformat recur_item_find_occurrence()
recur.c: Refactor/Reformat recur_item_find_occurrence()

Fix a couple of whitespace and line breaks. Bail out early instead of
using nested if statements.

Signed-off-by: Lukas Fleischer <af90e31281d8305af43dc616c5aaca3c7165f8a7@cryptocrack.de>

lfos/calcurse,lfos/calcurse,lfos/calcurse