nanosleep(2): don't tsleep(9) if timeout is empty

[Scott Cheloha]

ok?

Index: sys/kern/kern_time.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_time.c,v
retrieving revision 1.103
diff -u -p -r1.103 kern_time.c
--- sys/kern/kern_time.c        28 May 2018 18:05:42 -0000      1.103
+++ sys/kern/kern_time.c        24 Dec 2018 21:21:40 -0000
@@ -288,13 +288,18 @@ sys_nanosleep(struct proc *p, void *v, r
        if (rmtp)
                getnanouptime(&sts);
 
+       if (!timespecisset(&rqt)) {
+               error = 0;
+               goto out;
+       }
+
        error = tsleep(&nanowait, PWAIT | PCATCH, "nanosleep",
            MAX(1, tstohz(&rqt)));
        if (error == ERESTART)
                error = EINTR;
        if (error == EWOULDBLOCK)
                error = 0;
-
+out:
        if (rmtp) {
                getnanouptime(&ets);