Fix infinite recursion if wxGrid is modified from event handler

Calling wxGrid::{Insert,Delete}{Rows,Cols}() from wxEVT_GRID_CELL_CHANGE
event handler resulted in infinite recursion because it tried to hide
the grid editor control again, which resulted in another CELL_CHANGE
event being generated and so on.

Break this infinite recursion in the usual way, i.e. by updating the
state of wxGrid before invoking the user-defined event handler.

This required separating SaveEditControlValue() in 2 functions, the main
one retaining IsCellEditControlEnabled() check for compatibility, and
the new DoSaveEditControlValue() that can be called even after disabling
the editor.

Closes #2287.

Closes https://github.com/wxWidgets/wxWidgets/pull/1540

include/wx/generic/grid.h

@@ -2482,6 +2482,10 @@ private:
     void SetNativeHeaderColCount();
     void SetNativeHeaderColOrder();
 
+    // Unlike the public SaveEditControlValue(), this method doesn't check if
+    // the edit control is shown, but just supposes that it is.
+    void DoSaveEditControlValue();
+
     // these sets contain the indices of fixed, i.e. non-resizable
     // interactively, grid rows or columns and are NULL if there are no fixed
     // elements (which is the default)

src/generic/grid.cpp

@@ -6858,10 +6858,14 @@ void wxGrid::EnableCellEditControl( bool enable )
             SendEvent(wxEVT_GRID_EDITOR_HIDDEN);
 
             HideCellEditControl();
-            SaveEditControlValue();
 
-            // do it after HideCellEditControl()
-            m_cellEditCtrlEnabled = enable;
+            // do it after HideCellEditControl() but before invoking
+            // user-defined handlers invoked by DoSaveEditControlValue() to
+            // ensure that we don't enter infinite loop if any of them try to
+            // disable the edit control again.
+            m_cellEditCtrlEnabled = false;
+
+            DoSaveEditControlValue();
         }
     }
 }
@@ -7115,6 +7119,12 @@ void wxGrid::SaveEditControlValue()
 {
     if ( IsCellEditControlEnabled() )
     {
+        DoSaveEditControlValue();
+    }
+}
+
+void wxGrid::DoSaveEditControlValue()
+{
     int row = m_currentCellCoords.GetRow();
     int col = m_currentCellCoords.GetCol();
 
@@ -7142,7 +7152,6 @@ void wxGrid::SaveEditControlValue()
 
     editor->DecRef();
     attr->DecRef();
-    }
 }
 
 void wxGrid::OnHideEditor(wxCommandEvent& WXUNUSED(event))