ransac,find_rotzoom: add missing alloc check

Bug: aomedia:3276
Change-Id: I7d5de84b14451bb7ffbe0a9824ddbb8e38e27c88

av1/encoder/ransac.c

diff --git a/av1/encoder/ransac.c b/av1/encoder/ransac.c
index ff00a46..e849b34 100644
--- a/av1/encoder/ransac.c
+++ b/av1/encoder/ransac.c
@@ -225,6 +225,7 @@
 static int find_rotzoom(int np, double *pts1, double *pts2, double *mat) {
   const int np2 = np * 2;
   double *a = (double *)aom_malloc(sizeof(*a) * (np2 * 5 + 20));
+  if (a == NULL) return 1;
   double *b = a + np2 * 4;
   double *temp = b + np2;
   int i;