Fix use of uninitialized value in noise_util.c

BUG=aomedia:1963

Change-Id: If08601d556fbefbb680a2b9ecfd48115d32bef60

aom_dsp/noise_util.c

diff --git a/aom_dsp/noise_util.c b/aom_dsp/noise_util.c
index db4ca07..87e8e9f 100644
--- a/aom_dsp/noise_util.c
+++ b/aom_dsp/noise_util.c
@@ -75,6 +75,12 @@
     aom_noise_tx_free(noise_tx);
     return NULL;
   }
+  // Clear the buffers up front. Some outputs of the forward transform are
+  // real only (the imaginary component will never be touched)
+  memset(noise_tx->tx_block, 0,
+         2 * sizeof(*noise_tx->tx_block) * block_size * block_size);
+  memset(noise_tx->temp, 0,
+         2 * sizeof(*noise_tx->temp) * block_size * block_size);
   return noise_tx;
 }