Enable plugin window without trace opened

The plugin windows can now be opened without any trace file opened.

src/interface/Interface_graphic.cpp

@@ -814,23 +814,17 @@ void Interface_graphic::on_about_triggered(){
                           "</a>.<br /><br />"));
 }
 
-void Interface_graphic::on_show_plugins_triggered() {
-
-
-
-
-    if(_core->get_trace() != NULL) {
+void Interface_graphic::on_show_plugins_triggered()
+{
+    if(_plugin_window == NULL) { //Creation of the window
+        _plugin_window = new Plugin_window( _core, this );
+    }
 
-        if(_plugin_window == NULL) { //Creation of the window
-            _plugin_window = new Plugin_window(_core, this);
-        }
+    if( _core->get_trace() != NULL ) {
         _plugin_window->update_trace();
-        _plugin_window->show();
-        // TODO create actions as for the recent files menu in order to open at the good tab
-    }
-    else {
-        error("Must load a trace before applying plugins");
     }
+
+    _plugin_window->show();
 }