SaveTool: make the weapon part radio buttons match the game.

src/SaveTool/SaveTool_MassViewer_Weapons.cpp

@@ -429,7 +429,7 @@ void SaveTool::drawWeaponEditor(Weapon& weapon) {
                 _selectedWeaponPart = 0;
             }
             ImGui::SameLine();
-            ImGui::RadioButton(std::to_string(i + 1).c_str(), &_selectedWeaponPart, i);
+            ImGui::RadioButton(std::to_string(i).c_str(), &_selectedWeaponPart, i);
         }
 
         auto& part = weapon.parts[_selectedWeaponPart];