chg: reset errno prior to calling strtol() stable

chg: reset errno prior to calling strtol()

Otherwise we can't figure out if the last strtol() invocation failed or
not.

--- a/contrib/chg/chg.c	Tue Nov 03 11:15:50 2020 +0900
+++ b/contrib/chg/chg.c	Tue Nov 03 11:24:21 2020 +0900
@@ -276,6 +276,7 @@
 		debugmsg("closing files based on /proc contents");
 		struct dirent *de;
 		while ((de = readdir(dp))) {
+			errno = 0;
 			char *end;
 			long fd_value = strtol(de->d_name, &end, 10);
 			if (end == de->d_name) {