Simplify state switching and checking for OSTC3
Simplify state switching and checking for OSTC3

This simplifies the code to check and handle state switching for the
OSTC3.

Suggested-by: Jef Driesen <b15fddc167525de4ad1fb3bc376a47e585fa0068@libdivecomputer.org>
Signed-off-by: Anton Lundin <0a6ca81d300dbabb82140c80e76039139ef86644@acc.umu.se>

henrik242/libdivecomputer,Poltsi/libdivecomputer-vms,glance-/libdivecomputer,glance-/libdivecomputer,henrik242/libdivecomputer