utils: catch calloc memory failures in iio_stresstest

On error, calloc() returns NULL. Or a successful call to calloc() with nmemb
or size equal to zero.

In the past, we would not catch that, and just start operating on the
null pointer (crashing). So catch that, and gracefully error out.

Signed-off-by: Robin Getz <rgetz@mathworks.com>

tests/iio_stresstest.c

@@ -519,6 +519,12 @@ int main(int argc, char **argv)
 
 	ret = (void *)calloc(info.num_threads, sizeof(void *));
 
+	if (!ret || !info.start || !info.refills || !info.buffers || !info.starts ||
+			!info.tid || !info.threads) {
+		fprintf(stderr, "Memory allocation failure\n");
+		return 0;
+	}
+
 	for (i = 0; i < info.num_threads; i++) {
 		info.start[i] = malloc(NUM_TIMESTAMPS * sizeof(struct timeval));
 	}
@@ -658,6 +664,11 @@ int main(int argc, char **argv)
 		/* gather and sort things, so we can print out a histogram */
 		struct timeval *sort;
 		sort = calloc(info.num_threads * NUM_TIMESTAMPS, sizeof(struct timeval));
+		if (!sort) {
+			app_running = 0;
+			fprintf(stderr, "Memory allocation failure\n");
+			break;
+		}
 		b = 0;
 		/* gather */
 		for (i = 0; i < info.num_threads; i++) {