Add LookupBlockIndex function

src/validation.h

@@ -428,6 +428,13 @@ public:
 /** Replay blocks that aren't fully applied to the database. */
 bool ReplayBlocks(const CChainParams& params, CCoinsView* view);
 
+inline CBlockIndex* LookupBlockIndex(const uint256& hash)
+{
+    AssertLockHeld(cs_main);
+    BlockMap::const_iterator it = mapBlockIndex.find(hash);
+    return it == mapBlockIndex.end() ? nullptr : it->second;
+}
+
 /** Find the last common block between the parameter chain and a locator. */
 CBlockIndex* FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& locator);