sanitize trim($year) to avoid PHP warning

[JocelynDelalande]

The fact trim($year) was called without sanitization leads to log errors like:

ERROR - 2015-01-17 08:30:29 --> Severity: Warning  --> trim() expects parameter 1 to be string, array given /var/www/agendav/libs/icalcreator/iCalcreator.class.php 8639

While adding an event to the calendar from web interface.

Even worse, this output was bundled in the POST request response for event creation :

<p>Severity: Warning</p>
<p>Message:  trim() expects parameter 1 to be string, array given</p>
<p>Filename: icalcreator/iCalcreator.class.php</p>
<p>Line Number: 8638</p>
<p>Severity: Warning</p>
<p>Message:  trim() expects parameter 1 to be string, array given</p>
<p>Filename: icalcreator/iCalcreator.class.php</p>
<p>Line Number: 8638</p>

which leads to json parsing error.

This PR fixes that.

[JocelynDelalande]

Also reported upstream : iCalcreator/iCalcreator#12

[jorgelzpz]

@JocelynDelalande thank you for your detailed PR! Unfortunately, current development branch (develop) is using Sabre VObject instead of iCalcreator. I forgot to remove references to iCalcreator, but current develop branch doesn't use iCalcreator at all.

Thank you again!