Debugger: Avoid inconsistent state when killing LLDB

Avoid having a useless debugger if LLDB gets killed from outside QC.
Shut down the debugger engine instead.

Task-number: QTCREATORBUG-18723
Change-Id: I92f9b61c559ac43f1fc74af88861f35ca462f71f
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/debugger/lldb/lldbengine.cpp

@@ -743,6 +743,8 @@ void LldbEngine::handleLldbError(QProcess::ProcessError error)
     showMessage(QString("LLDB PROCESS ERROR: %1").arg(error));
     switch (error) {
     case QProcess::Crashed:
+        m_lldbProc.disconnect();
+        notifyEngineShutdownFinished();
         break; // will get a processExited() as well
     // impossible case QProcess::FailedToStart:
     case QProcess::ReadError: