e_aes.c: uninitialized variable in aes_ccm_init_key.

PR: 2874
Submitted by: Tomas Mraz

crypto/evp/e_aes.c

diff --git a/crypto/evp/e_aes.c b/crypto/evp/e_aes.c
index 519e014..5dccb2f 100644
--- a/crypto/evp/e_aes.c
+++ b/crypto/evp/e_aes.c
@@ -1218,6 +1218,7 @@
 			vpaes_set_encrypt_key(key, ctx->key_len*8, &cctx->ks);
 			CRYPTO_ccm128_init(&cctx->ccm, cctx->M, cctx->L,
 					&cctx->ks, (block128_f)vpaes_encrypt);
+			cctx->str = NULL;
 			cctx->key_set = 1;
 			break;
 			}