Fix compiler warnings
Fixes the following compiler warning
miner.cpp: In constructor ‘COrphan::COrphan(const CTransaction*)’: miner.cpp:69:14: warning: ‘COrphan::feeRate’ will be initialized after [-Wreorder] CFeeRate feeRate; ^ miner.cpp:68:12: warning: ‘double COrphan::dPriority’ [-Wreorder] double dPriority; ^ miner.cpp:71:5: warning: when initialized here [-Wreorder] COrphan(const CTransaction* ptxIn) : ptx(ptxIn), feeRate(0), dPriority(0)