Bug when sailing through single land bridges/hexes

[jt-traub]

The SailThroughCheck code does not correctly handle PREVENT_SAIL_THROUGH and ALLOW_TRIVIAL_PORTAGE which allows any ship to sail through any single land hex

; nw     /C   \     ne
;   ____/      \____
;  /A   \      /F   \
; /  ~ ~ \____/  ~ ~ \
; \ ~ ~  /D   \ ~ ~  /
;  \____/Thandi\____/
;  /B   \      /G   \
; /  ~ ~ \____/  ~ ~ \
; \ ~ ~  /E   \ ~ ~  /
;  \____/Hynoda\____/
;       \      /H   \
;        \____/  ~ ~ \
;             \ ~ ~  /
; sw           \____/ se

In the above, you can sail from B->D->F though when PREVENT_SAIL_THROUGH is 1 you shouldn't be able to.

[jt-traub]

Another report (from a different player) said that in a scenario sailing north->south with ocean->land->ocean they were stopped on the land hex, so I think there is a much more subtle bug here somewhere!!