Fix potential deadlock

[aguycalled]

This PR fixes a potential deadlock moving IsColdStakingEnabled() out of CheckTransaction().

2019-06-04 20:36:10  (1) cs_main  wallet/wallet.cpp:1965
2019-06-04 20:36:10  (2) cs_wallet  wallet/wallet.cpp:1965
2019-06-04 20:36:10 Current lock order is:
2019-06-04 20:36:10  (2) pwallet->cs_wallet  wallet/walletdb.cpp:633
2019-06-04 20:36:10  (1) cs_main  ./main.cpp:4589

[mxaddict]

utACK

[proletesseract]

compiling and testing now.

[proletesseract]

Compiles and runs on ubuntu 18.04. Test suite runs. Not entirely sure exactly how to test this specific change. Code looks fine. Can you perhaps just explain in a bit more detail what was wrong and what you did to fix it? If I understand correctly, having the cold staking check where it was before could cause a conflict in how the thread locking occurs resulting in this algorithm being unable to proceed?

[aguycalled]

IsColdStakingEnabled() locked cs_main while CheckTransaction() locks cs_wallet, so every call to CheckTransaction() was locking in the order cs_wallet,cs_main conflicting with the lock order from wallet/wallet.cpp:1965 which runs in parallel in other thread

[mxaddict]

Tested Ubuntu 18.04 ran node for 26 hours