ObjectList: Fixes

* Fixed update of a warning icon for multi-part object, when some part with errors was deleted
 * Fixed a crash when selecting non-Object and non-Volume item (in get_mesh_errors_info() was missed check of the obj_idx)

+ Follow-up 1cc7b4ba97 - some code refactoring:
  * fixed RepairedMeshErrors.merge()
  * get_mesh_errors_count() renamed to get_repaired_errors_count()

src/slic3r/GUI/GUI_ObjectManipulation.hpp

@@ -4,6 +4,7 @@
 #include <memory>
 
 #include "GUI_ObjectSettings.hpp"
+#include "GUI_ObjectList.hpp"
 #include "libslic3r/Point.hpp"
 #include <float.h>
 
@@ -194,7 +195,7 @@ public:
 #endif // __APPLE__
 
     void update_item_name(const wxString &item_name);
-    void update_warning_icon_state(const std::pair<wxString, std::string>& warning);
+    void update_warning_icon_state(const MeshErrorsInfo& warning);
     void msw_rescale();
     void sys_color_changed();
     void on_change(const std::string& opt_key, int axis, double new_value);