Core: correctly check usbi_read() returned value

For messages received on the hotplug pipe, the message was read via
usbi_read() (ssize_t) and compared against the size of the message
struct (size_t). usbi_read() returns -1 on an error condition, so some
systems can cast the ssize_t to size_t for the comparison, making it
equal to SIZE_MAX and causing the error check condition to incorrectly
evaluate to false.
2 files changed