Fix crash on space press when no surface selected in texture editing mode

src/Application/TextureMappingState.cpp

@@ -30,6 +30,10 @@ void TextureMappingState::onKeyPressed(Application * app, ofKeyEventArgs & args)
 		 break;
 	 
 	 case ' ':
+		 if(app->getSurfaceManager()->getSelectedSurface() == 0){
+			return;
+		 }
+		 
          if(app->getSurfaceManager()->getSelectedSurface()->getSource()->getType() ==
             SourceType::SOURCE_TYPE_VIDEO){
             app->getCmdManager()->exec(