Fix height of cursor inside insets

Fix height of cursor inside insets

It turns out that Cursor::getFont() does not return a fully realized
font in some cases. This patch uses real_current_font instead, which
seems better anyway.

I suspect that all uses of getFont() should be removed, but this is
not code that I know well.

Fixes bug #10478.
(cherry picked from commit b099d9ae15c45a9c30727078d69c0c7bd8029c9a)