Coverity fixes in core.c

CID 703181 (#1 of 1): Dereference before null check (REVERSE_INULL)check_after_deref: Null-checking vmi suggests that it may be null, but it has already been dereferenced on all paths leading to the check.
CID 1237203 (#1 of 1): Unchecked return value (CHECKED_RETURN)3. check_return: Calling arch_init without checking return value (as is done elsewhere 7 out of 8 times)