overload: Prefer passing literal 0 to ints instead of ptrs

Effectively this makes overload resolution a bit more permissive, and it
turns out that hCalcTypesDiff() returning a FB_OVLPROC_HALFMATCH score
for this case is a problem too, because it means that it will out-rank
any integer-to-integer matches, because those are scored via
FB_OVLPROC_HALFMATCH - symb_dtypeMatchTB..., which will always produce
lower values than FB_OVLPROC_HALFMATCH.

However, I think that integer parameters should be preferred over pointer
parameters when passing in an integer argument (even if it's a literal 0).
Thus hCalcTypesDiff() now returns 1 instead of FB_OVLPROC_HALFMATCH when
passing a literal 0 to a pointer. This should cause that case to be
allowed, but rated lower than normal integer-to-integer matches. Thus it
will only be the last resort, not the first choice.