core: fix a wrong assertion on decimal comparison with double

mp_compare_decimal_any_number erroneously assumed that any float or
double from which a decimal can't be created is either infinite or NaN.
This is not true. Any float greater than 1e38 can't fit into our decimal
representation. When such a float got compared to a decimal, an
assertion fired, which was wrong. Luckily, on release build the
comparison was correct. Only the assertion is wrong. Fix it.

Closes #8472

NO_DOC=bugfix