Don't start an already active dialogue event.

This will fix the Warning seen when dealing quickly with dialogues that have events triggered when beginning a line.

The BeginLine() function could be called more than once because of emotes of the use of the confirm key, but the begin event could also be triggered more than once when a short dialogue could be triggered several times.

Closes #82.

src/modes/map/map_dialogue.cpp

@@ -486,7 +486,7 @@ void DialogueSupervisor::_BeginLine()
     // Starts possible events at new line.
     MapMode *map_mode = MapMode::CurrentInstance();
     std::string line_event = _current_dialogue->GetLineBeginEvent(_line_counter);
-    if(!line_event.empty()) {
+    if(!line_event.empty() && !map_mode->GetEventSupervisor()->IsEventActive(line_event)) {
         map_mode->GetEventSupervisor()->StartEvent(line_event);
     }