[BUGFIX] Followup 2 to mod.SHARED.colPos_list fix

Deal with empty mod.SHARED and fill activeColPosList with colPosList
in case the TSconfig setting is empty.

Resolves: #39967
Releases: 6.2, 6.3
Change-Id: I5e2e4420de8f1d603e13a03758f97803e545d9a3
Reviewed-on: http://review.typo3.org/32743
Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Tested-by: Helmut Hummel <helmut.hummel@typo3.org>