Correct ProcessRequestQueue leak in VideoScan::SetDirs.

When QUERY_VIDEOS was called against the master backend, it would run
the video scanner, which would in turn pull the master backend hostname
from gCoreContext.  Since that queries the value from the master
backend, it would stall, never to return, and lock the attached
ProcessRequestQueue until the backend was restarted.

Author: wagnerrp

mythtv/libs/libmythmetadata/videoscan.cpp

@@ -90,7 +90,9 @@ VideoScannerThread::~VideoScannerThread()
 
 void VideoScannerThread::SetDirs(QStringList dirs)
 {
-    QString master = gCoreContext->GetMasterHostName();
+    QString master = gCoreContext->IsMasterBackend() ? 
+                            gCoreContext->GetHostName() :
+                            gCoreContext->GetMasterHostName();
     QStringList searchhosts, mdirs;
     m_offlineSGHosts.clear();