Fix locking in GetTransaction.

GetTransaction needs to lock cs_main until ReadBlockFromDisk completes, the data inside CBlockIndex's can change since pruning.  This lock was held by all calls to GetTransaction except rest_tx.

src/main.cpp

@@ -954,14 +954,13 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
 bool GetTransaction(const uint256 &hash, CTransaction &txOut, uint256 &hashBlock, bool fAllowSlow)
 {
     CBlockIndex *pindexSlow = NULL;
-    {
+
     LOCK(cs_main);
-        {
+
     if (mempool.lookup(hash, txOut))
     {
         return true;
     }
-        }
 
     if (fTxIndex) {
         CDiskTxPos postx;
@@ -995,7 +994,6 @@ bool GetTransaction(const uint256 &hash, CTransaction &txOut, uint256 &hashBlock
         if (nHeight > 0)
             pindexSlow = chainActive[nHeight];
     }
-    }
 
     if (pindexSlow) {
         CBlock block;