select: stop treating POLLRDBAND as an error

POLLRDBAND does not seem to be an general error and on Windows the value
for POLLIN is 768 and the value for POLLRDBAND is 512.

Fixes #10501
Reported-by: opensslonzos-github on github
Closes #10592

lib/select.c

@@ -230,14 +230,14 @@ int Curl_socket_check(curl_socket_t readfd0, /* two sockets to read from */
   if(readfd0 != CURL_SOCKET_BAD) {
     if(pfd[num].revents & (POLLRDNORM|POLLIN|POLLERR|POLLHUP))
       r |= CURL_CSELECT_IN;
-    if(pfd[num].revents & (POLLRDBAND|POLLPRI|POLLNVAL))
+    if(pfd[num].revents & (POLLPRI|POLLNVAL))
       r |= CURL_CSELECT_ERR;
     num++;
   }
   if(readfd1 != CURL_SOCKET_BAD) {
     if(pfd[num].revents & (POLLRDNORM|POLLIN|POLLERR|POLLHUP))
       r |= CURL_CSELECT_IN2;
-    if(pfd[num].revents & (POLLRDBAND|POLLPRI|POLLNVAL))
+    if(pfd[num].revents & (POLLPRI|POLLNVAL))
       r |= CURL_CSELECT_ERR;
     num++;
   }