Avoid duplicate CheckBlock checks

src/primitives/block.h

@@ -77,6 +77,9 @@ public:
     // network and disk
     std::vector<CTransaction> vtx;
 
+    // memory only
+    mutable bool fChecked;
+
     CBlock()
     {
         SetNull();
@@ -100,6 +103,7 @@ public:
     {
         CBlockHeader::SetNull();
         vtx.clear();
+        fChecked = false;
     }
 
     CBlockHeader GetBlockHeader() const