IsInitialBlockDownload no longer uses header-only timestamps.

This avoids a corner case (mostly visible on testnet) where bogus
 headers can keep nodes in IsInitialBlockDownload.

src/main.cpp

@@ -1744,11 +1744,10 @@ bool IsInitialBlockDownload()
         return true;
     if (chainActive.Tip()->nChainWork < UintToArith256(chainParams.GetConsensus().nMinimumChainWork))
         return true;
-    bool state = (chainActive.Height() < pindexBestHeader->nHeight - 24 * 6 ||
+    if (chainActive.Tip()->GetBlockTime() < (GetTime() - nMaxTipAge))
-            std::max(chainActive.Tip()->GetBlockTime(), pindexBestHeader->GetBlockTime()) < GetTime() - nMaxTipAge);
+        return true;
-    if (!state)
     latchToFalse.store(true, std::memory_order_relaxed);
-    return state;
+    return false;
 }
 
 bool fLargeWorkForkFound = false;