Attempting to sort a bug search results page by the Votes column results in an Internal Server Error.  The problem doesn't occur when attempting to sort by any other column (at least among the ones I've tested).

Steps to reproduce:
1. Go to <https://bugs.kde.org/query.cgi> and run an Advanced Search.  For example, <https://bugs.kde.org/buglist.cgi?bug_status=UNCONFIRMED&bug_status=CONFIRMED&bug_status=ASSIGNED&bug_status=REOPENED&chfield=[Bug%20creation]&chfieldfrom=2016-08-15&chfieldto=Now&product=kmail2&product=kontact&query_format=advanced&votes=1&votes_type=greaterthaneq>
2. Click on the header of the "Votes" column to sort the results by number of votes.  (If this column doesn't appear, then use the "Change columns" button at the bottom of the page to add it first.)

Observed behaviour:
3. A page with the following message appears:

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator at sysadmin@kde.org to inform them of the time this error occurred, and the actions you performed just before this error.

More information about this error may be available in the server error log.
Apache/2.4.7 (Ubuntu) Server at bugs.kde.org Port 443