Bug 343194 DnD month view: Error if event is dragged out of displayed calendar date range, r=dmose

calendar/base/content/calendar-month-view.xml

@@ -450,8 +450,9 @@
               dropbox.setAttribute("dropbox", "true");
               dropbox.setAttribute("flex", "1");
 
-              var box = this.monthView.findBoxForDate(shadowStart).box;
-              box.dayitems.insertBefore(dropbox, box.dayitems.firstChild);
+              var box = this.monthView.findBoxForDate(shadowStart);
              if (!box) {
                  // Dragging to the end of a view
+                  shadowStart.day += 1;
+                  shadowStart.normalize();
                  continue;
              }
              box.box.dayitems.insertBefore(dropbox, box.box.dayitems.firstChild);
               this.monthView.mDropShadows.push(dropbox);
 
               shadowStart.day += 1;