When no payload is set for `crlf_apply` we try to compute the
crlf attributes ourselves with `crlf_check`. When the function
determines that the current file does not require any treatment
we return the GIT_PASSTHROUGH error code without actually
allocating the out-pointer, which indicates the file should not
be passed through the filter.

The `crlf_apply` function explicitly checks for the
GIT_PASSTHROUGH return code and ignores it. This means we will
try to apply the crlf-filter to the current file, leading us to
dereference the unallocated payload-pointer.

Fix this obviously incorrect behavior by not treating
GIT_PASSTHROUGH in any special way. This is the correct thing to
do anyway, as the code indicates that the file should not be
passed through the filter.