mincurses.c: use cursor_normal to disable cursor_invisible
There are actually three capabilities:
cursor_invisible
cursor_normal
cursor_visible
The "cursor_normal" string disables both "cursor_invisible" and
"cursor_visible". The actual meaning of "cursor_visible" is to
make the cursor "very visible."
Prefer using "cursor_normal" to disable "cursor_invisible".
Not all terminals have a "cursor_visible" string and it's not the
opposite of "cursor_invisible" anyway.
In the off chance that a terminal description has been created
incorrectly, if "cursor_normal" is not available but "cursor_visible"
is, it will be used instead (just like the previous code did).
Signed-off-by: 
Kyle J. McKay <mackyle@gmail.com>