correct snprintf truncation check in closefrom()

Truncation cannot happen unless the system has set PATH_MAX to some
nonsensically low value.

bz#2862, patch from Daniel Le

openbsd-compat/bsd-closefrom.c

@@ -77,7 +77,7 @@ closefrom(int lowfd)
 
     /* Check for a /proc/$$/fd directory. */
     len = snprintf(fdpath, sizeof(fdpath), "/proc/%ld/fd", (long)getpid());
-    if (len > 0 && (size_t)len <= sizeof(fdpath) && (dirp = opendir(fdpath))) {
+    if (len > 0 && (size_t)len < sizeof(fdpath) && (dirp = opendir(fdpath))) {
 	while ((dent = readdir(dirp)) != NULL) {
 	    fd = strtol(dent->d_name, &endp, 10);
 	    if (dent->d_name != endp && *endp == '\0' &&