Move QUERY_FILETRANSFER handling to improve backend performance.

This significantly reduces the backend CPU usage for me when streaming a
recording or other file to the frontend.

Each time we send a command to the backend we perform a number of string
comparisons to find the correct handler. In the cases where that same command
is sent regularly, maybe several times a second those comparisons can stack up
to result in a high CPU load. This can be avoided by moving the most frequently
used commands to the top of the list thereby avoiding a couple of dozen or more
comparisons each time.

There may be other commands that should be moved to the top with similar
benefit.

mythtv/programs/mythbackend/mainserver.cpp

@@ -434,7 +434,14 @@ void MainServer::ProcessRequestWork(MythSocket *sock)
     pbs->IncrRef();
     sockListLock.unlock();
 
-    if (command == "QUERY_RECORDINGS")
+    if (command == "QUERY_FILETRANSFER")
+    {
+        if (tokens.size() != 2)
+            LOG(VB_GENERAL, LOG_ERR, "Bad QUERY_FILETRANSFER");
+        else
+            HandleFileTransferQuery(listline, tokens, pbs);
+    }
+    else if (command == "QUERY_RECORDINGS")
     {
         if (tokens.size() != 2)
             LOG(VB_GENERAL, LOG_ERR, "Bad QUERY_RECORDINGS query");
@@ -632,13 +639,6 @@ void MainServer::ProcessRequestWork(MythSocket *sock)
     {
         HandleGetRecorderNum(listline, pbs);
     }
-    else if (command == "QUERY_FILETRANSFER")
-    {
-        if (tokens.size() != 2)
-            LOG(VB_GENERAL, LOG_ERR, "Bad QUERY_FILETRANSFER");
-        else
-            HandleFileTransferQuery(listline, tokens, pbs);
-    }
     else if (command == "QUERY_GENPIXMAP2")
     {
         HandleGenPreviewPixmap(listline, pbs);