Fix bugnot line.strip() or  with multiline values

The URL that showed this error up was

https://mozorg.cdn.mozilla.net/media/caldata/GermanHolidays.ics

with the following entry:

BEGIN:VEVENT
CREATED:20061023T132503Z
LAST-MODIFIED:20101214T141313Z
DTSTAMP:20101214T141313Z
UID:917544590
SUMMARY:Heilige drei Könige
STATUS:CONFIRMED
RRULE:FREQ=YEARLY;BYMONTH=1
CATEGORIES:Feiertag
DTSTART;VALUE=DATE:20060106
DTEND;VALUE=DATE:20060107
DESCRIPTION:Christlicher Feiertag. Nur in Baden-Württemberg\, Bayern und
 Sachsen-Anhalt.
X-MOZ-GENERATION:1
END:VEVENT