Don't crash if a calender contains an all-day event

src/appointment.rs

@@ -240,11 +240,10 @@ fn parse_dates(params: Option<Vec<(String, Vec<String>)>>, value: &str) -> Vec<D
 		.map(|(_, values)| values)
 		.filter(|values| values.len() == 1)
 		.next()
-		.unwrap()
-		.into_iter()
-		.next()
-		.unwrap();
-	let tz: chrono_tz::Tz = if let Ok(tz) = tz.parse() {
+		.and_then(|values| values.into_iter().next())
+		.and_then(|tz| tz.parse().ok());
+
+	let tz: chrono_tz::Tz = if let Some(tz) = tz {
 		tz
 	} else {
 		return vec![];