Stop using dtstart when dtend is not defined

Goocalendar supports to have None as value for end date so we must use it if
dtend is not defined.
Also it is better to fail directly on missing dtstart attribute.

issue5786
review32431002

tryton/gui/window/view_form/view/calendar_.py

@@ -82,8 +82,8 @@ class ViewCalendar(View):
         self.screen.switch_view('form')
 
     def on_event_released(self, goocalendar, event):
-        dtstart = self.attributes.get('dtstart')
-        dtend = self.attributes.get('dtend') or dtstart
+        dtstart = self.attributes['dtstart']
+        dtend = self.attributes.get('dtend')
         record = event.record
         group = record.group
         previous_start = record[dtstart].get(record)
@@ -93,12 +93,12 @@ class ViewCalendar(View):
             new_start = event.start.date()
             new_end = event.end.date() if event.end else None
         if previous_start <= new_start:
-            if new_end:
+            if dtend:
                 group.fields[dtend].set_client(record, new_end)
             group.fields[dtstart].set_client(record, new_start)
         else:
             group.fields[dtstart].set_client(record, new_start)
-            if new_end:
+            if dtend:
                 group.fields[dtend].set_client(record, new_end)
         goocalendar.select(new_start)
         record.save()

tryton/gui/window/view_form/view/calendar_gtk/calendar_.py

@@ -19,7 +19,7 @@ class Calendar_(goocalendar.Calendar):
         self.current_domain_period = self.get_displayed_period()
 
     def set_default_date(self, record, selected_date):
-        dtstart = self.attrs.get('dtstart')
+        dtstart = self.attrs['dtstart']
         record[dtstart].set(record, datetime.datetime.combine(selected_date,
             datetime.time(0)))
 
@@ -50,7 +50,7 @@ class Calendar_(goocalendar.Calendar):
     def current_domain(self):
         first_datetime, last_datetime = \
             self.current_domain_period.get_dates(True)
-        dtstart = self.attrs.get('dtstart')
+        dtstart = self.attrs['dtstart']
         dtend = self.attrs.get('dtend') or dtstart
         domain = ['OR',
             ['AND', (dtstart, '>=', first_datetime),
@@ -62,8 +62,8 @@ class Calendar_(goocalendar.Calendar):
         return domain
 
     def display(self, group):
-        dtstart = self.attrs.get('dtstart')
-        dtend = self.attrs.get('dtend') or dtstart
+        dtstart = self.attrs['dtstart']
+        dtend = self.attrs.get('dtend')
         if self.screen.current_record:
             record = self.screen.current_record
             date = record[dtstart].get(record)
@@ -81,7 +81,10 @@ class Calendar_(goocalendar.Calendar):
                 continue
 
             start = record[dtstart].get_client(record)
-            end = record[dtend].get_client(record)
+            if dtend:
+                end = record[dtend].get_client(record)
+            else:
+                end = None
             midnight = datetime.time(0)
             all_day = False
             if not isinstance(start, datetime.datetime):