TerminalPanel: Disconnect destroyed signal in destructor

Otherwise, when QObject cleanup, which runs after our destructor,
destroys the terminalPart, it would call back into us
when we're already half-destroyed.

This trips an assert in Qt "Called object is not of the correct
type (class destructor may have already run)"

src/panels/terminal/terminalpanel.cpp

@@ -47,6 +47,9 @@ TerminalPanel::TerminalPanel(QWidget *parent)
 
 TerminalPanel::~TerminalPanel()
 {
+    // Avoid when QObject cleanup, which comes after our destructor, deletes the konsolePart
+    // and subsequently calls back into our slot when the destructor has already run.
+    disconnect(m_konsolePart, &KParts::ReadOnlyPart::destroyed, this, &TerminalPanel::terminalExited);
 }
 
 void TerminalPanel::goHome()