Fix overload index mismatch in overloading logic.

Fix overload index mismatch in overloading logic.

In amagic_call(), the 'method' arg comes the overload enum in overload.h, but is expected to match the bit set from %overloading::numbers::names. It values wrongly start at 1, differing by 1 from the enum indexes. This didn't appear in the tests because 'method' was reduced modulo 7 instead of 8.