fix(utc): handle short UTC offset format without minutes

[CYRyo]

Summary

utcOffset('+08') and utcOffset('-05') return NaN instead of the correct offset in minutes.

The validation regex REGEX_VALID_OFFSET_FORMAT correctly accepts short offsets like +08 (minutes are optional via (?::?\d\d)?), but the parsing regex REGEX_OFFSET_HOURS_MINUTES_FORMAT only captures ['+', '08'] — minutesOffset is undefined, causing (+8 * 60) + (+undefined) = NaN.

Reproduction

dayjs().utcOffset('+08')    // broken: internal offset becomes NaN
dayjs().utcOffset('+08:00') // works: 480
dayjs().utcOffset('-05')    // broken: NaN
dayjs().utcOffset('-05:00') // works: -300

Fix

Default minutesOffset to 0 when no minutes group is captured:

- const totalOffsetInMinutes = (+hoursOffset * 60) + (+minutesOffset)
+ const totalOffsetInMinutes = (+hoursOffset * 60) + (+(minutesOffset || 0))