Avoid selecting all rows up to UINT_MAX in generic wxDataViewCtrl.

Shift clicking in a control with multiple selections without a previous
current row attempted to select all rows from the current one up to UINT_MAX
which resulted in a program freezing (and probably running out of memory in 64
bit builds).

Fix this by explicitly checking for the absence of the current item.

Closes #16582.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@77941 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/datavgen.cpp

@@ -4359,6 +4359,13 @@ void wxDataViewMainWindow::OnMouse( wxMouseEvent &event )
                 unsigned int lineFrom = oldCurrentRow,
                     lineTo = current;
 
+                if ( lineFrom == static_cast<unsigned>(-1) )
+                {
+                    // If we hadn't had any current row before, treat this as a
+                    // simple click and select the new row only.
+                    lineFrom = current;
+                }
+
                 if ( lineTo < lineFrom )
                 {
                     lineTo = lineFrom;