m_FontSize is in 1..7 range, not 0..6, so add 1 to it when setting it from the
index into m_FontsSizes array.
Also update the comment explaining the valid range of m_FontsSize.
Closes#14442.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71878 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775