Avoid events when implicitly selecting first wxBookCtrl page.

The first page added to a wxBookCtrlBase-derived control is always selected,
even if "bSelect" argument of AddPage() was false. This is necessary because
a non-empty book control must always have a selection but the "selection
changed" event generated when doing it is unexpected.

Fix this by not generating any events when the first page is implicitly
selected.

Closes #12075.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65967 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/bookctrl.h

@@ -252,6 +252,17 @@ protected:
     // choose the default border for this window
     virtual wxBorder GetDefaultBorder() const { return wxBORDER_NONE; }
 
+    // After the insertion of the page in the method InsertPage, calling this
+    // method sets the selection to the given page or the first one if there is
+    // still no selection. The "selection changed" event is sent only if
+    // bSelect is true, so when it is false, no event is sent even if the
+    // selection changed from wxNOT_FOUND to 0 when inserting the first page.
+    //
+    // Returns true if the selection was set to the specified page (explicitly
+    // because of bSelect == true or implicitly because it's the first page) or
+    // false otherwise.
+    bool DoSetSelectionAfterInsertion(size_t n, bool bSelect);
+
     // set the selection to the given page, sending the events (which can
     // possibly prevent the page change from taking place) if SendEvent flag is
     // included