windows: Restore behaviour of skipping malformed device GUIDs

Previously when getting the device list, a malformed device GUID would
be explicitly ignored and skipped, allowing the operation to complete. A
recent change to winusb_get_device_list() in commit fdab67b accidentally
changed this behaviour, so this scenario instead caused an early exit
with error code LIBUSB_ERROR_NO_MEM.

Closes #1475
2 files changed