[Qt] use BitcoinGUI::DEFAULT_WALLET constant in bitcoin.cpp
[Qt] use BitcoinGUI::DEFAULT_WALLET constant in bitcoin.cpp

(cherry picked from commit 314fbd9ac7713e812e85960499474dcf453b563e)

reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin