queryWindowInfo: Differenciate between unmannaged and user cancel
Previous fix here didn't take into account the case where use can cancel the query (by pressing Esc).
Quick test:
qdbus org.kde.KWin /KWin org.kde.KWin.showDebugConsole
qdbus org.kde.KWin /KWin org.kde.KWin.queryWindowInfo [Click on Console]
Error: org.kde.KWin.Error.InvalidWindow
Tried to query information about an unmanaged window
qdbus org.kde.KWin /KWin org.kde.KWin.queryWindowInfo [ESC]
Error: org.kde.KWin.Error.UserCancel
User cancelled the query
Requires fix in: !402 (merged)