BUG/MEDIUM: sample: make the CPU and latency sample fetches check for a stream

cpu_calls, cpu_ns_avg, cpu_ns_tot, lat_ns_avg and lat_ns_tot depend on the
stream to find the current task and must check for it or they may cause a
crash if misused or used in a log-format string after commit 5f940703b3
("MINOR: log: Don't depends on a stream to process samples in log-format
string").

This must be backported as far as 1.9.

(cherry picked from commit e0dd210cea36972a6f566b9b49d8f0c33340df99)
Signed-off-by: Willy Tarreau <w@1wt.eu>
(cherry picked from commit 4080b9e6cd272301077d85b5bfb79d5e76cc3864)
Signed-off-by: Willy Tarreau <w@1wt.eu>
diff --git a/src/sample.c b/src/sample.c
index 77b420c..1bc0de9 100644
--- a/src/sample.c
+++ b/src/sample.c
@@ -2970,6 +2970,9 @@
 static int
 smp_fetch_cpu_calls(const struct arg *args, struct sample *smp, const char *kw, void *private)
 {
+	if (!smp->strm)
+		return 0;
+
 	smp->data.type = SMP_T_SINT;
 	smp->data.u.sint = smp->strm->task->calls;
 	return 1;
@@ -2979,6 +2982,9 @@
 static int
 smp_fetch_cpu_ns_avg(const struct arg *args, struct sample *smp, const char *kw, void *private)
 {
+	if (!smp->strm)
+		return 0;
+
 	smp->data.type = SMP_T_SINT;
 	smp->data.u.sint = smp->strm->task->calls ? smp->strm->task->cpu_time / smp->strm->task->calls : 0;
 	return 1;
@@ -2988,6 +2994,9 @@
 static int
 smp_fetch_cpu_ns_tot(const struct arg *args, struct sample *smp, const char *kw, void *private)
 {
+	if (!smp->strm)
+		return 0;
+
 	smp->data.type = SMP_T_SINT;
 	smp->data.u.sint = smp->strm->task->cpu_time;
 	return 1;
@@ -2997,6 +3006,9 @@
 static int
 smp_fetch_lat_ns_avg(const struct arg *args, struct sample *smp, const char *kw, void *private)
 {
+	if (!smp->strm)
+		return 0;
+
 	smp->data.type = SMP_T_SINT;
 	smp->data.u.sint = smp->strm->task->calls ? smp->strm->task->lat_time / smp->strm->task->calls : 0;
 	return 1;
@@ -3006,6 +3018,9 @@
 static int
 smp_fetch_lat_ns_tot(const struct arg *args, struct sample *smp, const char *kw, void *private)
 {
+	if (!smp->strm)
+		return 0;
+
 	smp->data.type = SMP_T_SINT;
 	smp->data.u.sint = smp->strm->task->lat_time;
 	return 1;