add upper bound to the padding option

src/cli.rs

@@ -40,6 +40,7 @@ pub struct Args {
 pub enum CliError {
     CouldNotParseTime,
     CouldNotParseDate,
+    PaddingTooLarge,
     CouldNotParseTimezone(String),
     CouldNotGenerateTimetable(String),
 }
@@ -49,6 +50,7 @@ impl fmt::Display for CliError {
         let message = match *self {
             Self::CouldNotParseTime => "Couldn't parse time".to_string(),
             Self::CouldNotParseDate => "Couldn't parse date".to_string(),
+            Self::PaddingTooLarge => "Padding option cannot be larger than 12".to_string(),
             Self::CouldNotParseTimezone(ref tz) => {
                 format!("Couldn't parse timezone {}", tz).to_string()
             }
@@ -70,6 +72,10 @@ pub fn print_timezones(
     local_timezone: &String,
     padding_hours: i8,
 ) -> Result<(), CliError> {
+    if padding_hours > 12 {
+        return Err(CliError::PaddingTooLarge);
+    };
+
     let parsed_time = if let Some(t) = time {
         if let Ok(hour) = t.parse::<u32>() {
             NaiveTime::from_hms_opt(hour, 0, 0).ok_or(CliError::CouldNotParseTime)?