Extend the range of the main lock.

It was possible for the used data structures to be modified by the
block acceptor thread while used by the stake thread. This could
result in a crash, see gridcoin-community#865.

src/miner.cpp

@@ -851,7 +851,6 @@ void StakeMiner(CWallet *pwallet)
 
     while (!fShutdown)
     {
-
         //wait for next round
         MilliSleep(nMinerSleep);
 
@@ -880,6 +879,10 @@ void StakeMiner(CWallet *pwallet)
             continue;
         }
 
+        // Lock main lock since GetNextProject and subsequent calls
+        // require the state to be static.
+        LOCK(cs_main);
+
         GetNextProject(true);
 
         // * Create a bare block
@@ -920,7 +923,6 @@ void StakeMiner(CWallet *pwallet)
         }
 
         // * delegate to ProcessBlock
-        LOCK(cs_main);
         if (!ProcessBlock(NULL, &StakeBlock, true))
         {
             { LOCK(MinerStatus.lock);