KeyError: 'LOCATION'

The file at the end of this issue leads to a crash:

```
$ python3 ical2csv.py noloc.ics
UID,CREATED,LAST-MODIFIED,DTSTART,DTEND,SUMMARY,LOCATION
Traceback (most recent call last):
File "ical2csv.py", line 148, in
args.include_full_day):
File "ical2csv.py", line 56, in process
item['LOCATION'] = item['LOCATION'].replace(',', ';')
File "/usr/local/lib/python3.5/dist-packages/icalendar/caselessdict.py", line 42, in __getitem__
return super(CaselessDict, self).__getitem__(key.upper())
KeyError: 'LOCATION'
```

----

```
BEGIN:VCALENDAR
PRODID:-//Mozilla.org/NONSGML Mozilla Calendar V1.1//EN
VERSION:2.0
BEGIN:VTIMEZONE
TZID:Europe/Berlin
BEGIN:DAYLIGHT
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
DTSTART:19700329T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
TZNAME:CET
DTSTART:19701025T030000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
END:STANDARD
END:VTIMEZONE

BEGIN:VEVENT
CREATED:20160715T134945Z
LAST-MODIFIED:20160718T074326Z
DTSTAMP:20160718T074326Z
UID:16CC71D0-3938-484A-8348-D450D5A3AEC5
SUMMARY:test
STATUS:CONFIRMED
DTSTART;TZID=Europe/Berlin:20160718T090000
DTEND;TZID=Europe/Berlin:20160719T140000
SEQUENCE:0
X-DEFAULT-ALARM:TRUE
END:VEVENT

END:VCALENDAR
```