Fix txfm_stage_range_check

Only check cos_bit range if cos_bit is not NULL

Change-Id: I286fc056812b20242cc962a8b008af7093d05b1d

test/av1_txfm_test.cc

@@ -367,18 +367,14 @@ void txfm_stage_range_check(const int8_t *stage_range, int stage_num,
                             int high_range) {
   for (int i = 0; i < stage_num; ++i) {
     EXPECT_LE(stage_range[i], low_range);
+    if (cos_bit != NULL) {
+      ASSERT_LE(stage_range[i] + cos_bit[i], high_range) << "stage = " << i;
+    }
   }
   for (int i = 0; i < stage_num - 1; ++i) {
     // make sure there is no overflow while doing half_btf()
-    EXPECT_LE(stage_range[i] + cos_bit[i], high_range);
-    EXPECT_LE(stage_range[i + 1] + cos_bit[i], high_range);
-    if (stage_range[i] + cos_bit[i] > high_range) {
-      std::cout << i;
-      assert(0);
-    }
-    if (stage_range[i + 1] + cos_bit[i] > high_range) {
-      std::cout << i;
-      assert(0);
+    if (cos_bit != NULL) {
+      ASSERT_LE(stage_range[i + 1] + cos_bit[i], high_range) << "stage = " << i;
     }
   }
 }