Handle empty 'keys' attributes
The 'key' sysfs attribte is present for a device if a) the thunderbolt controller is in secure
mode (SL2) and b) the device supports identity verification. If both conditions are true but no key was yet used by userspace to do said identity verification the key
sysfs attribute is empty; NB: the contents of the key
file will always have a trailing newline, even if empty.
Change bolt_key_load_file
so that reading an empty ("" or single whitespace character) files is not an error but will result in NULL
with no GError
being set. Add tests for it.
Closes #121 (closed)