Fix netplay on modern versions of Visual Studio, from Ala-lala

sc2/src/uqm/supermelee/netplay/netrcv.c

@@ -146,12 +146,12 @@ dataReadyCallback(NetDescriptor *nd) {
 		}
 
 		if (numRead == -1) {
-			switch (errno) {
-				case EAGAIN:  // No more data for now.
-					return;
-				case EINTR:  // System call was interrupted. Retry.
-					continue;
-				default: {
+			if (errno == EWOULDBLOCK || errno == EAGAIN)
+				return;  // No more data for now.
+			else if (errno == EINTR)
+				continue;  // System call was interrupted. Retry.
+			else
+			{
 				int savedErrno = errno;
 				log_add(log_Error, "recv() failed: %s.\n",
 						strerror(errno));
@@ -160,7 +160,6 @@ dataReadyCallback(NetDescriptor *nd) {
 				return;
 			}
 		}
-		}
 
 		conn->readEnd += numRead;