Work around QTBUG-56382 with manual event loop flushing

* See https://bugreports.qt.io/browse/QTBUG-56382 for more details -
  creating DXGI swapchains adds a windows hook, and enough windows hooks
  forces out Qt's internal hook which it relies upon for proper event
  processing.

qrenderdoc/Code/CaptureContext.cpp

@@ -62,6 +62,11 @@ CaptureContext::~CaptureContext()
   delete m_MainWindow;
 }
 
+bool CaptureContext::isRunning()
+{
+  return m_MainWindow && m_MainWindow->isVisible();
+}
+
 void CaptureContext::LoadLogfile(QString logFile, bool temporary)
 {
   LoadLogfile(-1, "", logFile, temporary);