[hwasan] Fix a possible null dereference problem (#77737)

This is clearly a copy-paste mistake, fix it with this patch.
After checking the `local.function_name` is not null, it should check
the len for `local.function_name`, not `local.name`. And this could lead
to possible null dereference since the second
`internal_strlen(local.name)` does not guarantee `local.name` is not
null.