capitalize Infinite tooltip in Elements panel of Math

Change-Id: I15e5a7c9a37a4908adcdc0d3396c82845e442b66
Reviewed-on: https://gerrit.libreoffice.org/13346
Reviewed-by: Wesley J. Landaker <wjl@icecavern.net>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>