Don't crash in wxAuiToolBar::GetToolBarFits().

The code could crash if m_overflowVisible was true but m_overflowSizerItem was
NULL. Ideally this shouldn't happen in the first place, but it did, so at
least fix the crash for now -- and hopefully this code will be refactored to
make it more clear later.

Backport from trunk, see #15747.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75399 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -588,6 +588,7 @@ All (GUI):
 - Fix wxCommandProcessor::IsDirty() return value which was wrong after undoing
   all commands without saving (Neil Chittenden).
 - Fix crash when Destroy()-ing a TLW with non-TLW parent.
+- Fix crash in wxAuiToolBar::GetToolBarFits().
 
 wxGTK:
 

src/aui/auibar.cpp

@@ -1772,7 +1772,7 @@ bool wxAuiToolBar::GetToolFitsByIndex(int tool_idx) const
     if (m_orientation == wxVERTICAL)
     {
         // take the dropdown size into account
-        if (m_overflowVisible)
+        if (m_overflowVisible && m_overflowSizerItem)
             cli_h -= m_overflowSizerItem->GetSize().y;
 
         if (rect.y+rect.height < cli_h)
@@ -1781,7 +1781,7 @@ bool wxAuiToolBar::GetToolFitsByIndex(int tool_idx) const
     else
     {
         // take the dropdown size into account
-        if (m_overflowVisible)
+        if (m_overflowVisible && m_overflowSizerItem)
             cli_w -= m_overflowSizerItem->GetSize().x;
 
         if (rect.x+rect.width < cli_w)