[FIX] calendar: r_date must be defined before use

commit b4ec51021b forgot about the case where no domain was supplied
or when the conditions on it were not fulfilled.

before this commit, a traceback was thrown and no event was shown

After this commit, no errors and all the relevant events are shown

opw 782985

addons/calendar/calendar.py

@@ -1197,6 +1197,7 @@ class calendar_event(osv.Model):
                 # check if there are one False
                 pile = []
                 ok = True
+                r_date = None
                 for arg in domain:
                     if str(arg[0]) in ('start', 'stop', 'final_date'):
                         if str(arg[0]) == 'start':