fdo#64150 don't segfault when there is no line

Change-Id: Iab36de3d407925cdb0e092afae457907f0261b3e
Reviewed-on: https://gerrit.libreoffice.org/3765Reviewed-by: Thorsten Behrens <tbehrens@suse.com>
Tested-by: Thorsten Behrens <tbehrens@suse.com>

editeng/source/items/frmitems.cxx

@@ -1966,7 +1966,8 @@ bool SvxBoxItem::PutValue( const uno::Any& rVal, sal_uInt8 nMemberId )
                 for (int n(0); n != SAL_N_ELEMENTS(aBorders); ++n)
                 {
                     editeng::SvxBorderLine* pLine = const_cast< editeng::SvxBorderLine* >( GetLine( aBorders[n] ) );
-                    pLine->SetWidth( nWidth );
+                    if( pLine )
+                        pLine->SetWidth( nWidth );
                 }
             }
             return sal_True;