fix a memory leak in key.cpp
fix a memory leak in key.cpp

- add EC_KEY_free() in CKey::Reset() when pkey != NULL
- init pkey with NULL in CKey constructor

PaycoinFoundation/paycoin,LambocoinFoundation/Lambocoin,PaycoinFoundation/paycoin,ligerzero459/paycoin,LambocoinFoundation/Lambocoin,thommyV91/Suck-a-Coin,mitchellcash/paycoin,PaycoinFoundation/paycoin,IngCr3at1on/paycoin,IngCr3at1on/paycoin,ligerzero459/paycoin,ligerzero459/paycoin,LambocoinFoundation/Lambocoin,LambocoinFoundation/Lambocoin,IngCr3at1on/paycoin,ligerzero459/paycoin,PaycoinFoundation/paycoin,mitchellcash/paycoin,thommyV91/Suck-a-Coin,IngCr3at1on/paycoin,thommyV91/Suck-a-Coin,mitchellcash/paycoin,mitchellcash/paycoin,thommyV91/Suck-a-Coin