Debugger: Normalize some state handling

Remove some now-unusual connection to RunControl::finished
and use a finished() callback in the ToolRunner implementation
instead.

Change-Id: Ieddf05a2258d9a300ac50a739d77d9cfaee10ca6
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/debuggerplugin.cpp

@@ -2957,6 +2957,8 @@ void DebuggerPluginPrivate::runControlStarted(DebuggerEngine *engine)
 
 void DebuggerPluginPrivate::runControlFinished(DebuggerEngine *engine)
 {
+    if (engine)
+        engine->handleFinished();
     if (m_shuttingDown)
         return;
     showStatusMessage(tr("Debugger finished."));