Don't recycle DocumentInserter, create a new one every time

After all, everyone else using DocumentInserter across the codebase
does the same.

For KDE4, an attempt to reuse the same filepicker dialog sporadically
crashes in the depths of (old-ish, possibly buggy) libQt due to nested
event loop and/or recursive repaints.

(crash scenario: Calc > Sheet > Link to external data > Browse > double-click
a file > Browse again > Kaboom!)

Change-Id: Ib494203abd07873919b8394a442f09c5329d237c
Reviewed-on: https://gerrit.libreoffice.org/49082Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>

sc/source/ui/inc/linkarea.hxx

@@ -46,7 +46,7 @@ private:
     VclPtr<OKButton>     m_pBtnOk;
 
     ScDocShell*             pSourceShell;
-    sfx2::DocumentInserter* pDocInserter;
+    std::unique_ptr<sfx2::DocumentInserter> pDocInserter;
 
     SfxObjectShellRef   aSourceRef;
 

sc/source/ui/miscdlgs/linkarea.cxx

@@ -83,8 +83,7 @@ void ScLinkedAreaDlg::dispose()
 
 IMPL_LINK_NOARG(ScLinkedAreaDlg, BrowseHdl, Button*, void)
 {
-    if ( !pDocInserter )
-        pDocInserter = new sfx2::DocumentInserter(this, ScDocShell::Factory().GetFactoryName());
+    pDocInserter.reset( new sfx2::DocumentInserter(this, ScDocShell::Factory().GetFactoryName()) );
     pDocInserter->StartExecuteModal( LINK( this, ScLinkedAreaDlg, DialogClosedHdl ) );
 }