Fix Equihash state initialisation in miner

After a new block is found or after a few nonces have been tried (currently
after every nonce), the miner checks for global changes. If any of these are
triggered, a new block is built from scratch, which re-initialises the Equihash
input. But if none of the checks are triggered, the miner just updates nTime and
continues mining - without updating the Equihash input to account for the new
block header. This bugfix corrects the behaviour by regenerating the Equihash
input in both situations.

src/miner.cpp

@@ -486,6 +486,7 @@ void static BitcoinMiner(CWallet *pwallet)
             int64_t nStart = GetTime();
             arith_uint256 hashTarget = arith_uint256().SetCompact(pblock->nBits);
 
+            while (true) {
                 // Hash state
                 crypto_generichash_blake2b_state state;
                 eh.InitialiseState(state);
@@ -498,7 +499,6 @@ void static BitcoinMiner(CWallet *pwallet)
                 // H(I||...
                 crypto_generichash_blake2b_update(&state, (unsigned char*)&ss[0], ss.size());
 
-            while (true) {
                 // Find valid nonce
                 while (true)
                 {