Fix memory leak on exception in Key::SignCompact

src/key.cpp

@@ -328,7 +328,10 @@ bool CKey::SignCompact(uint256 hash, std::vector<unsigned char>& vchSig)
         }
 
         if (nRecId == -1)
+        {
+            ECDSA_SIG_free(sig);
             throw key_error("CKey::SignCompact() : unable to construct recoverable key");
+        }
 
         vchSig[0] = nRecId+27+(fCompressedPubKey ? 4 : 0);
         BN_bn2bin(sig->r,&vchSig[33-(nBitsR+7)/8]);