#175 broken map behaviour

[Roman M. Parparov]

When running map over a sea region which contains
_known_ sea sectors,
but doesn't contain owned sectors (shore) map output is
empty.

Consider:
eic [27:281]% map -10:-5,-10:-5
1-----
098765
-10 -10
-9 -9
-8 -8
-7 -7
-6 . -6
-5 . + -5
1-----
098765

eic [28:281]% map -10:-6,-10:-5
1----
09876
-10 -10
-9 -9
-8 -8
-7 -7
-6 -6
-5 -5
1----

[Marc Olzheim]

Logged In: YES
user_id=763555

Seeing the hardcoded bitmaps in src/lib/subs/getbit.c I
guess it's enough to add a border of 3 around the requested
map, calculate it and skip the border of 3 again, thus
having sectors in the borders fill the bitmap...
Is this set of hardcoded bitmaps up to a range of 3
something we still want to have lingering around for now, or
should this be fixed with a more general solution ?