capitalize Infinite tooltip in Elements panel of Math

Change-Id: I6bb19e199c1014536e967d427b966afd8ecd0302
Reviewed-on: https://gerrit.libreoffice.org/13345
Reviewed-by: Wesley J. Landaker <wjl@icecavern.net>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>