Display priority todo items above regular items
Display priority todo items above regular items

We now support todo items with undefined priority and currently display
them above todo items with a strictly positive priority. Change this and
always list items with a priority greater than zero first.

Signed-off-by: Lukas Fleischer <c9ca73f8336dcfb037ec2c2abf52d80a6847a5cd@calcurse.org>

lfos/calcurse,lfos/calcurse,lfos/calcurse