Test malloc, set unused to NULL if it fails

---
 tests/heapshrink-helper.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/tests/heapshrink-helper.c
+++ b/tests/heapshrink-helper.c
@@ -21,5 +21,7 @@
 
 static void __attribute__((constructor)) setup_heapshrink_helper(void)
 {
-	(void) malloc(1);
+	void *unused = malloc(1);
+	if (unused)
+		unused = NULL;
 }