tdf#120703 PVS: Check potentially null pointer before use

V595 The 'pHdl' pointer was utilized before it was verified against nullptr.
     Check lines: 192, 197.

Change-Id: I52e1d1eadaded8616b8a27e0fcfaf6d1e6baa03e
Reviewed-on: https://gerrit.libreoffice.org/71455
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

sc/source/ui/view/cellsh3.cxx

@@ -182,7 +182,7 @@ void ScCellShell::Execute( SfxRequest& rReq )
                                                   GetViewData()->GetTabNo(),
                                                   aStr );
                     }
-                    else
+                    else if (pHdl)
                     {
                         SC_MOD()->SetInputMode(SC_INPUT_TABLE);