Show as many tabs in wxAuiNotebook as possible

Currently, when a tab is closed in wxAuiNotebook, the tabs are not moved right
to use free space (on the right side of he rightmost tab), which requires
clicking "left" button to make tabs visible.

This commit changes the behaviour to keep as many tabs shown as possible.

Closes #17233.

src/aui/auibook.cpp

@@ -431,6 +431,10 @@ void wxAuiTabContainer::Render(wxDC* raw_dc, wxWindow* wnd)
     if (!dc.IsOk())
         return;
 
+    // ensure we show as many tabs as possible
+    while (m_tabOffset > 0 && IsTabVisible(page_count-1, m_tabOffset-1, &dc, wnd))
+        --m_tabOffset;
+
     // find out if size of tabs is larger than can be
     // afforded on screen
     int total_width = 0;