gui: use fallback value for Version and User Agent during peer connection
gui: use fallback value for Version and User Agent during peer connection

During connection setup for a peer, getpeerinfo returns "version": 0, "subver": ""
and the GUI Peers window displays 0 and an empty field, respectively.

Give these fields the same behavior as the other fields in the GUI Peers window:
display the fallback value in src/qt/forms/debugwindow.ui (i.e. "N/A") until a
valid result is available after the peer connection completes.

jambolo/bitcoin,bitcoinsSG/bitcoin,lateminer/bitcoin,jambolo/bitcoin,mruddy/bitcoin,bitcoin/bitcoin,jambolo/bitcoin,kallewoof/bitcoin,sipsorcery/bitcoin,namecoin/namecoin-core,namecoin/namecoin-core,lateminer/bitcoin,sipsorcery/bitcoin,bitcoinsSG/bitcoin,kallewoof/bitcoin,fanquake/bitcoin,namecoin/namecoin-core,kallewoof/bitcoin,bitcoin/bitcoin,tecnovert/particl-core,AkioNak/bitcoin,fanquake/bitcoin,lateminer/bitcoin,kallewoof/bitcoin,mruddy/bitcoin,tecnovert/particl-core,namecoin/namecoin-core,tecnovert/particl-core,tecnovert/particl-core,bitcoin/bitcoin,particl/particl-core,bitcoinsSG/bitcoin,sipsorcery/bitcoin,bitcoinsSG/bitcoin,particl/particl-core,namecoin/namecoin-core,sstone/bitcoin,sstone/bitcoin,namecoin/namecoin-core,jambolo/bitcoin,bitcoinsSG/bitcoin,sstone/bitcoin,lateminer/bitcoin,mruddy/bitcoin,mruddy/bitcoin,sstone/bitcoin,bitcoin/bitcoin,sstone/bitcoin,sipsorcery/bitcoin,fanquake/bitcoin,tecnovert/particl-core,bitcoinsSG/bitcoin,sstone/bitcoin,AkioNak/bitcoin,bitcoin/bitcoin,fanquake/bitcoin,AkioNak/bitcoin,fanquake/bitcoin,sipsorcery/bitcoin,AkioNak/bitcoin,jambolo/bitcoin,particl/particl-core,mruddy/bitcoin,particl/particl-core,mruddy/bitcoin,sipsorcery/bitcoin,particl/particl-core,particl/particl-core,AkioNak/bitcoin,lateminer/bitcoin,jambolo/bitcoin,kallewoof/bitcoin,bitcoin/bitcoin,AkioNak/bitcoin,tecnovert/particl-core,kallewoof/bitcoin,lateminer/bitcoin,fanquake/bitcoin