Fix: IS_SUBROOM_INDEX range

[entrez]

The macro (currently unused, I think) for checking whether a particular index designates a subroom was off by one on the maximum allowable value.

Because of the dedicated extra space for the g.rooms array terminator flag (hx == -1), subroom indices in g.rooms are set out in the range [MAXNROFROOMS+1, MAXNROFROOMS*2], inclusive.

Also some minor formatting tweaks.