Debugger: Some infrastructure for stricter watch model testing

Targeting re-use for tooltips, and potentially sorting.

Change-Id: I1ce8f4da73ab5ca13cd70d7c651bc76c67f91a39
Reviewed-by: hjk <hjk121@nokiamail.com>

src/libs/utils/basetreeview.cpp

@@ -136,6 +136,8 @@ void BaseTreeView::resizeColumnsToContents()
 
 void BaseTreeView::setAlwaysResizeColumnsToContents(bool on)
 {
+    if (!header())
+        return;
     QHeaderView::ResizeMode mode = on
         ? QHeaderView::ResizeToContents : QHeaderView::Interactive;
     for (int i = 0, n = header()->count(); i != n; ++i)