Make sure forked process has stopped when deleting MythSystem

This forces a termination in a forked MythSystem process when the
MythSystem object is destroyed, preventing a situation where the private
internal object tries to access resources from the no-longer-existent
parent object.

Fixes #11412

mythtv/libs/libmythbase/mythsystem.cpp

@@ -159,6 +159,11 @@ MythSystem::MythSystem(const MythSystem &other) :
 // QBuffers may also need freeing
 MythSystem::~MythSystem(void)
 {
+    if (GetStatus() == GENERIC_EXIT_RUNNING)
+    {
+        d->Term(true);
+        d->Wait();
+    }
     d->DecrRef();
 }