tdf#115438 Fix freeze when pasting unformatted text

ImpConnectParagraphs calls TextModified, which calculates the selection rectangles of
the paragraph for accessibility services by calling DrawSelectionXOR. When
calling ImpConnectParagraphs from ImpDeleteSelection, the selection isn't
valid, because UpdateSelection wasn't called yet. DrawSelectionXOR ends up
freezing the application, because pEndNode isn't valid.

This can be fixed by calling EnterBlockNotifications, to deliver the notification
sent by TextModified when the insertion is done.

Change-Id: Ia3a0e5b59a28f3503cbc54da682fcdaa5af277be
Reviewed-on: https://gerrit.libreoffice.org/57286Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

editeng/source/editeng/impedit2.cxx

@@ -624,7 +624,9 @@ bool ImpEditEngine::MouseMove( const MouseEvent& rMEvt, EditView* pView )
 
 EditPaM ImpEditEngine::InsertText(const EditSelection& aSel, const OUString& rStr)
 {
+    EnterBlockNotifications();
     EditPaM aPaM = ImpInsertText( aSel, rStr );
+    LeaveBlockNotifications();
     return aPaM;
 }