silly web server: silent a compilation warning

Recent gcc warns when byte count of strncpy() equals the destination
buffer size. Since the destination buffer is previously cleared and
the source string is always shorter, reducing the byte count by one
silents the warning without affecting the result.

Closes curl#5059

Author: monnerat

tests/server/sws.c

@@ -2163,7 +2163,7 @@ int main(int argc, char *argv[])
   case AF_UNIX:
     memset(&me.sau, 0, sizeof(me.sau));
     me.sau.sun_family = AF_UNIX;
-    strncpy(me.sau.sun_path, unix_socket, sizeof(me.sau.sun_path));
+    strncpy(me.sau.sun_path, unix_socket, sizeof(me.sau.sun_path) - 1);
     rc = bind(sock, &me.sa, sizeof(me.sau));
     if(0 != rc && errno == EADDRINUSE) {
       struct stat statbuf;