Core: fix the not found error when type the kernel name without the extent.

Core: fix the not found error when type the kernel name without the extent.

it will not clear the zf flag when not found the right file, so it will give the
next file search(searching for a different filename extentsion the wrong answer,
so we need do it after every file searching.

well, in fact we should use EAX(the file lenght in bytes) or si(the open_file_t
structure pointer) to indicate if we have successfully found the file or not.