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).

(cherry picked from commit 08e0a79aeba6fd41cbb51de3be48659619f27206)

Conflicts:
	cui/source/dialogs/SpellDialog.cxx

Change-Id: I1c310c028aaaf774431d0b1e6bba10e901a8166d