[posix] fix handling SPI interrupts (#4607)
[posix] fix handling SPI interrupts (#4607)

When SPI is already interrupted before select(), the wait timeout will
be set to 0, and select() will return 0 immediately if there are no
new events. As a result, cause an incorrect OT_ERROR_RESPONSE_TIMEOUT
error.

This commit fixes this issue by check if data is ready before checking
the select() result.
librasungirl/openthread,jwhui/openthread,lanyuwen/openthread,jwhui/openthread,chshu/openthread,librasungirl/openthread,chshu/openthread,lanyuwen/openthread,lanyuwen/openthread,srickardti/openthread,abtink/openthread,bukepo/openthread,jwhui/openthread,lanyuwen/openthread,bukepo/openthread,chshu/openthread,jwhui/openthread,abtink/openthread,openthread/openthread,srickardti/openthread,lanyuwen/openthread,chshu/openthread,bukepo/openthread,openthread/openthread,librasungirl/openthread,chshu/openthread,chshu/openthread,librasungirl/openthread,lanyuwen/openthread,abtink/openthread,srickardti/openthread,bukepo/openthread,openthread/openthread,srickardti/openthread,abtink/openthread,openthread/openthread