Merge bitcoin-core#583: JNI: fix use sig array

74e2dbd JNI: fix use sig array (liuyujun)

Pull request description:

ACKs for commit 74e2db:
  sipa:
    ACK 74e2dbd. This is clearly an improvement.
  real-or-random:
    ACK 74e2dbd I've read the code but haven't tested it

Tree-SHA512: 850b32e893463be4be28185dcc127d429afe4b6076036a078b7c61d590e0f4ea89127e448760b71c087cf70ffbefc52d87db77a5131bee81f3e4f95cfbd3bd3e

Author: sipa

src/java/org_bitcoin_NativeSecp256k1.c

@@ -81,15 +81,15 @@ SECP256K1_API jobjectArray JNICALL Java_org_bitcoin_NativeSecp256k1_secp256k1_1e
   jbyteArray sigArray, intsByteArray;
   unsigned char intsarray[2];
 
-  secp256k1_ecdsa_signature sig[72];
+  secp256k1_ecdsa_signature sig;
 
-  int ret = secp256k1_ecdsa_sign(ctx, sig, data, secKey, NULL, NULL);
+  int ret = secp256k1_ecdsa_sign(ctx, &sig, data, secKey, NULL, NULL);
 
   unsigned char outputSer[72];
   size_t outputLen = 72;
 
   if( ret ) {
-    int ret2 = secp256k1_ecdsa_signature_serialize_der(ctx,outputSer, &outputLen, sig ); (void)ret2;
+    int ret2 = secp256k1_ecdsa_signature_serialize_der(ctx,outputSer, &outputLen, &sig ); (void)ret2;
   }
 
   intsarray[0] = outputLen;