Don't push/pop disabled SVS subgoal states

When SVS is disabled for subgoals, don't push or pop the state stack as new
subgoals are created.

Core/SVS/src/svs.cpp

@@ -384,6 +384,11 @@ void svs::state_creation_callback(Symbol* state)
     std::string type, msg;
     svs_state* s;
 
+    if (!(state->is_top_state() || is_enabled_in_substates()))
+    {
+        return;
+    }
+
     if (state_stack.empty())
     {
         if (scn_cache)
@@ -404,6 +409,12 @@ void svs::state_creation_callback(Symbol* state)
 void svs::state_deletion_callback(Symbol* state)
 {
     svs_state* s;
+
+    if (!(state->is_top_state() || is_enabled_in_substates()))
+    {
+        return;
+    }
+
     s = state_stack.back();
     assert(state == s->get_state());
     if (state_stack.size() == 1)