lib/tst_test.c: fix case of hitting tst_vbrk_ before setup_ipc

We can hit TBROK/TCONF before call to setup_ipc(), for example
a TCONF in kernel version check, in which case do_exit() tries
to use NULL pointer 'results'.

Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
Signed-off-by: Jan Stancek <jstancek@redhat.com>
diff --git a/lib/tst_test.c b/lib/tst_test.c
index c560727..4f417ea 100644
--- a/lib/tst_test.c
+++ b/lib/tst_test.c
@@ -445,20 +445,22 @@
 
 static void do_exit(int ret)
 {
-	printf("\nSummary:\n");
-	printf("passed   %d\n", results->passed);
-	printf("failed   %d\n", results->failed);
-	printf("skipped  %d\n", results->skipped);
-	printf("warnings %d\n", results->warnings);
+	if (results) {
+		printf("\nSummary:\n");
+		printf("passed   %d\n", results->passed);
+		printf("failed   %d\n", results->failed);
+		printf("skipped  %d\n", results->skipped);
+		printf("warnings %d\n", results->warnings);
 
-	if (results->failed)
-		ret |= TFAIL;
+		if (results->failed)
+			ret |= TFAIL;
 
-	if (results->skipped)
-		ret |= TCONF;
+		if (results->skipped)
+			ret |= TCONF;
 
-	if (results->warnings)
-		ret |= TWARN;
+		if (results->warnings)
+			ret |= TWARN;
+	}
 
 	do_cleanup();