spell dialog: Make [Close] work in protected documents with editable fields.

We have to call ToggleChildWindow directly; calling SfxDispatcher's Execute()
does not work here when we are in a document with protected section - in that
case, the cursor can move from the editable field to the protected area, and
the slots get disabled because of SW_DISABLE_ON_PROTECTED_CURSOR (see
FN_SPELL_GRAMMAR_DIALOG in .sdi).

Change-Id: I1c310c028aaaf774431d0b1e6bba10e901a8166d
Reviewed-on: https://gerrit.libreoffice.org/13531
Reviewed-by: Andras Timar <andras.timar@collabora.com>
Tested-by: Andras Timar <andras.timar@collabora.com>