tdf#119561: fix assert when double click field in a table

by calling ClearMark so we clean table cursor and related stuff
before creating a new cursor for field edition
See https://bugs.documentfoundation.org/attachment.cgi?id=145578

Change-Id: I3a67fc5704d7a565f76e486bb12e4012e3336062
Reviewed-on: https://gerrit.libreoffice.org/61632
Tested-by: Jenkins
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>
diff --git a/sw/source/ui/fldui/fldedt.cxx b/sw/source/ui/fldui/fldedt.cxx
index 59df562..353f634 100644
--- a/sw/source/ui/fldui/fldedt.cxx
+++ b/sw/source/ui/fldui/fldedt.cxx
@@ -132,6 +132,7 @@ void SwFieldEditDlg::Init()

        // Traveling only when more than one field
        pSh->StartAction();
        pSh->ClearMark();
        pSh->CreateCursor();

        bool bMove = rMgr.GoNext();