Fix segfaults on bogus localtime input.

Fix segfaults on bogus localtime input.

The return code from localtime() function (and also gmtime() one)
wasn't checked. In some (rare) cases, it can return a NULL pointer
resulting in a segmentation fault.
The return code is now checked, but no specific action is performed
anyway.

Original patch from Ivana Varekova from RedHat (04/10/2010):
diff -up sysstat-9.0.6.1/sar.c.pom sysstat-9.0.6.1/sar.c
--- sysstat-9.0.6.1/sar.c.pom	2009-10-17 15:08:21.000000000 +0200
+++ sysstat-9.0.6.1/sar.c	2010-10-04 12:21:13.383442188 +0200
@@ -247,7 +247,7 @@ void reverse_check_act(unsigned int act_
  * @curr	Index in array for current sample statistics.
  ***************************************************************************
 */
-void sar_get_record_timestamp_struct(int curr)
+int  sar_get_record_timestamp_struct(int curr)
 {
 	struct tm *ltm;

@@ -257,10 +257,17 @@ void sar_get_record_timestamp_struct(int
 		rectime.tm_hour = record_hdr[curr].hour;
 		rectime.tm_min  = record_hdr[curr].minute;
 		rectime.tm_sec  = record_hdr[curr].second;
+		return 0;
 	}
 	else {
 		ltm = localtime((const time_t *) &record_hdr[curr].ust_time);
+
+		/* localtime procedure could not finish successful */
+		if (ltm == NULL)
+			return 1;
+
 		rectime = *ltm;
+		return 0;
 	}
 }

@@ -312,13 +319,17 @@ int check_line_hdr(void)
  * @cur_time	Timestamp string.
  ***************************************************************************
 */
-void set_record_timestamp_string(int curr, char *cur_time, int len)
+int set_record_timestamp_string(int curr, char *cur_time, int len)
 {
+	int ret;
 	/* Fill timestamp structure */
-	sar_get_record_timestamp_struct(curr);
+	ret = sar_get_record_timestamp_struct(curr);
+	if (ret != 0)
+		return ret;

 	/* Set cur_time date value */
 	strftime(cur_time, len, "%X", &rectime);
+	return 0;
 }

 /*
@@ -407,6 +418,7 @@ int write_stats(int curr, int read_from_
 		int use_tm_end, int reset, unsigned int act_id)
 {
 	int i;
+	int ret;
 	unsigned long long itv, g_itv;
 	static int cross_day = 0;
 	static __nr_t cpu_nr = -1;
@@ -423,9 +435,14 @@ int write_stats(int curr, int read_from_
 	}

 	/* Set previous timestamp */
-	set_record_timestamp_string(!curr, timestamp[!curr], 16);
+	ret = set_record_timestamp_string(!curr, timestamp[!curr], 16);
+	if (ret != 0)
+		return ret;
+
 	/* Set current timestamp */
-	set_record_timestamp_string(curr,  timestamp[curr],  16);
+	ret = set_record_timestamp_string(curr,  timestamp[curr],  16);
+	if (ret != 0)
+		return ret;

 	/* Check if we are beginning a new day */
 	if (use_tm_start && record_hdr[!curr].ust_time &&
@@ -569,8 +586,11 @@ int sar_print_special(int curr, int use_
 {
 	char cur_time[26];
 	int dp = 1;
+	int ret;

-	set_record_timestamp_string(curr, cur_time, 26);
+	ret = set_record_timestamp_string(curr, cur_time, 26);
+	if (ret != 0)
+		return ret;

 	/* The record must be in the interval specified by -s/-e options */
 	if ((use_tm_start && (datecmp(&rectime, &tm_start) < 0)) ||
@@ -865,7 +885,8 @@ void read_stats_from_file(char from_file
 				 */
 				read_file_stat_bunch(act, 0, ifd, file_hdr.sa_nr_act,
 						     file_actlst);
-				sar_get_record_timestamp_struct(0);
+				if (sar_get_record_timestamp_struct(0))
+					continue;
 			}
 		}
 		while ((rtype == R_RESTART) || (rtype == R_COMMENT) ||