Backport to fixes/0.24.

Release scheduler lock while running startup/shutdown commands.

Temporarily release the scheduler lock while running any external
startup or shutdown commands.  This allows those commands to query the
backend to get the current schedule if needed.  Fixes #9363.

mythtv/programs/mythbackend/scheduler.cpp

@@ -1820,6 +1820,8 @@ void Scheduler::RunScheduler(void)
 
                 if (firstRun)
                 {
+                    firstRun = false;
+
                     //the parameter given to the startup_cmd. "user" means a user
                     // started the BE, 'auto' means it was started automatically
                     QString startupParam = "user";
@@ -1853,9 +1855,12 @@ void Scheduler::RunScheduler(void)
                     if (!startupCommand.isEmpty())
                     {
                         startupCommand.replace("$status", startupParam);
+                        schedLock.unlock();
                         myth_system(startupCommand);
+                        schedLock.lock();
+                        if (reclist_changed)
+                            continue;
                     }
-                    firstRun = false;
                 }
 
                 PutInactiveSlavesToSleep();
@@ -2428,10 +2433,12 @@ void Scheduler::ShutdownServer(int prerollseconds, QDateTime &idleSince)
                                     "this computer :-\n\t\t\t\t\t\t") + halt_cmd);
 
         // and now shutdown myself
-        if (!myth_system(halt_cmd))
+        schedLock.unlock();
+        unsigned int res = myth_system(halt_cmd);
+        schedLock.lock();
+        if (!res)
             return;
-        else
-            VERBOSE(VB_IMPORTANT, "ServerHaltCommand failed, shutdown aborted");
+        VERBOSE(VB_IMPORTANT, "ServerHaltCommand failed, shutdown aborted");
     }
 
     // If we make it here then either the shutdown failed