Fix crash in wxAuiNotebook after dragging a page

Fix using outdated click position in wxAuiTabCtrl mouse handlers, which
resulted in an invalid wxEVT_AUINOTEBOOK_DRAG_MOTION event being
generated and a crash while handling it.

Ensure that we reset m_clickPt when resetting m_isDragging too so that
we don't decide that we're dragging if the mouse enters the window with
the left button already pressed after a previous drag.

See #24027, #24039.

(cherry picked from commit f1a3816cd9da0c3c7ceebe9735d37fb2d3158388)

docs/changes.txt

@@ -242,6 +242,7 @@ All:
 
 All (GUI):
 
+- Fix possible crash when dragging pages in wxAuiNotebook (#24027).
 - Fix refreshing multiple selection items in generic wxListCtrl.
 
 wxGTK:

src/aui/auibook.cpp

@@ -1099,6 +1099,7 @@ void wxAuiTabCtrl::OnCaptureLost(wxMouseCaptureLostEvent& WXUNUSED(event))
 {
     if (m_isDragging)
     {
+        m_clickPt = wxDefaultPosition;
         m_isDragging = false;
 
         wxAuiNotebookEvent evt(wxEVT_AUINOTEBOOK_CANCEL_DRAG, m_windowId);
@@ -1116,6 +1117,7 @@ void wxAuiTabCtrl::OnLeftUp(wxMouseEvent& evt)
 
     if (m_isDragging)
     {
+        m_clickPt = wxDefaultPosition;
         m_isDragging = false;
 
         wxAuiNotebookEvent e(wxEVT_AUINOTEBOOK_END_DRAG, m_windowId);