Add a function to wait for any key press

Introduce a new function keys_wait_for_any_key() and use it instead of
wgetch() whenever the return value is discarded.

Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

src/ui-calendar.c

@@ -658,7 +658,7 @@ void ui_calendar_change_day(int datefmt)
 			}
 			if (wrong_day) {
 				status_mesg(mesg_line1, mesg_line2);
-				wgetch(win[KEY].p);
+				keys_wait_for_any_key(win[KEY].p);
 			}
 		}
 	}