Reset row and columns count in wxRichTextTable::ClearTable().

No real changes, just update the internal variables in ClearTable() to avoid
inconsistent internal state, even if this doesn't seem to result in any
problems for now.

Closes #15190.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74057 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/richtext/richtextbuffer.cpp

@@ -10087,6 +10087,8 @@ void wxRichTextTable::ClearTable()
 {
     m_cells.Clear();
     DeleteChildren();
+    m_rowCount = 0;
+    m_colCount = 0;
 }
 
 bool wxRichTextTable::CreateTable(int rows, int cols)