Refactor wxTextEntry to use MSWEnsureHasAutoCompleteData()

The new function has more clear semantics than GetOrCreateCompleter()
which both returned the completer value and set m_autoCompleteData to it
as a side effect. MSWEnsureHasAutoCompleteData() still does the latter,
but returns just a boolean indicating whether it succeeded or failed,
making using it more straightforward.

No real changes.

include/wx/msw/textentry.h

@@ -100,9 +100,9 @@ private:
     // be called and the default implementation asserts if this is not the case.
     virtual void MSWProcessSpecialKey(wxKeyEvent& event);
 
-    // Get the auto-complete object creating it if necessary. Returns NULL if
-    // creating it failed.
-    wxTextAutoCompleteData *GetOrCreateCompleter();
+    // Check that we have auto-complete data, creating it if necessary. Returns
+    // false if creating it failed.
+    bool MSWEnsureHasAutoCompleteData();
 
     // Various auto-completion-related stuff, only used if any of AutoComplete()
     // methods are called. Use the function above to access it.