add missing error checking for various allocations

Bug: None
Test: `make check` passes
Change-Id: I4a60cca7167b61f61e2987a1c2bff05b53b31238

util.c

diff --git a/util.c b/util.c
index 48c3059..7cee515 100644
--- a/util.c
+++ b/util.c
@@ -434,7 +434,8 @@
 	/* One extra char for '/' and one for '\0', hence + 2. */
 	pathlen = strlen(external_path) + strlen(internal_path) + 2;
 	path = malloc(pathlen);
-	snprintf(path, pathlen, "%s/%s", external_path, internal_path);
+	if (path)
+		snprintf(path, pathlen, "%s/%s", external_path, internal_path);
 
 	return path;
 }