Merge bitcoin-core/gui#673: Use fallback value for Version and User Agent during peer connection

c2a21c0 gui: use fallback value for Version and User Agent during peer connection (Jon Atack)

Pull request description:

  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.

  An alternative would be to display nothing for both, as is the case currently for User Agent.

ACKs for top commit:
  jarolrod:
    ACK c2a21c0
  furszy:
    code ACK c2a21c0

Tree-SHA512: 4f0060fa9abde120a2bb48c9dcc87894d9bb70c33e6ab43b22400a4bcd0ceff0fa098adf7f385b0a7a4cf5d7053463b36fe1232e19a8d5025eecd8db9833f73b

Author: MacroFake

src/qt/rpcconsole.cpp

@@ -1178,8 +1178,12 @@ void RPCConsole::updateDetailWidget()
     ui->peerPingTime->setText(GUIUtil::formatPingTime(stats->nodeStats.m_last_ping_time));
     ui->peerMinPing->setText(GUIUtil::formatPingTime(stats->nodeStats.m_min_ping_time));
     ui->timeoffset->setText(GUIUtil::formatTimeOffset(stats->nodeStats.nTimeOffset));
-    ui->peerVersion->setText(QString::number(stats->nodeStats.nVersion));
-    ui->peerSubversion->setText(QString::fromStdString(stats->nodeStats.cleanSubVer));
+    if (stats->nodeStats.nVersion) {
+        ui->peerVersion->setText(QString::number(stats->nodeStats.nVersion));
+    }
+    if (!stats->nodeStats.cleanSubVer.empty()) {
+        ui->peerSubversion->setText(QString::fromStdString(stats->nodeStats.cleanSubVer));
+    }
     ui->peerConnectionType->setText(GUIUtil::ConnectionTypeToQString(stats->nodeStats.m_conn_type, /*prepend_direction=*/true));
     ui->peerNetwork->setText(GUIUtil::NetworkToQString(stats->nodeStats.m_network));
     if (stats->nodeStats.m_permission_flags == NetPermissionFlags::None) {