Fixed a crash when "resources/shapes" directory doesn't exist.

+ Localization for the "Internal error: %1%" in generic_exception_handle()

src/slic3r/GUI/GUI_App.cpp

@@ -608,7 +608,7 @@ static void generic_exception_handle()
         std::terminate();
         throw;
     } catch (const std::exception& ex) {
-        wxLogError("Internal error: %s", wxString::FromUTF8(ex.what()));
+        wxLogError(format_wxstr(_L("Internal error: %1%"), ex.what()));
         BOOST_LOG_TRIVIAL(error) << boost::format("Uncaught exception: %1%") % ex.what();
         throw;
     }