More defensive checking of value for seed height.

configure.ac

@@ -280,7 +280,7 @@ AX_CHECK_COMPILE_FLAG([-maes],[[AES_CFLAGS="-maes"]],[[AES_CFLAGS="no"]],[[$CXXF
 if  test x$AES_CFLAGS = xno; then
   AC_MSG_ERROR("Compiler does not support -maes which is required by Cryptonight.")
 fi
-CFLAGS="$CXXFLAGS $AES_CFLAGS"
+CFLAGS="$CFLAGS $AES_CFLAGS"
 
 TEMP_CXXFLAGS="$CXXFLAGS"
 CXXFLAGS="$CXXFLAGS $SSE42_CXXFLAGS"

src/primitives/block.cpp

@@ -20,13 +20,16 @@ extern "C" void cn_fast_hash(const void *data, size_t length, char *hash);
 static void cn_get_block_hash_by_height(uint64_t seed_height, char cnHash[32])
 {
     CBlockIndex* pblockindex = chainActive[seed_height];
-    if (pblockindex == NULL) {
+    if (pblockindex == nullptr) {
         // This will happen during initial block downloading, or when we
         // are out of sync by more than at least SEEDHASH_EPOCH_BLOCKS blocks.
         LOCK(cs_main);
-        pblockindex = mapBlockSeedHeight.find(seed_height)->second;
+        std::map<uint64_t, CBlockIndex*>::iterator iter = mapBlockSeedHeight.find(seed_height);
+        if (iter != mapBlockSeedHeight.end()) {
+            pblockindex = iter->second;
         }
-    if (pblockindex == NULL) {
+    }
+    if (pblockindex == nullptr) {
         return;
     }
     uint256 blockHash = pblockindex->GetBlockHash();