Fix (RTU USB) failure to `select()` an invalid file descriptor#1

Merged

jimklimov merged 5 commits intonetworkupstools:rtu_usbfrom

jimklimov:issue-nut-2609

Jan 14, 2025

Commits on Jan 11, 2025

src/modbus.c: _modbus_receive_msg(): avoid select() on invalid file descriptor
jimklimov
committed

Commits on Jan 12, 2025

configure.ac, src/modbus-rtu-usb.c: try to use libusb_get_pollfds() if available
jimklimov
committed
src/modbus.c: _modbus_receive_msg(): do not return after failed select() if this backend had no valid FD
jimklimov
committed

Commits on Jan 14, 2025