Broken: Blender 2.83 rB830a45a18a71: Improve usage of recent golden ratio define

When the AO pass is selected in the viewport and the user turns off the AO pass the viewport will still show that no pass is selected. In this case we should select the combined pass for rendering.

• Change in the RNA to show the Combined Pass when a Pass isn't valid anymore (item_get function)
• Change the renderpass to select the combined pass when the selection isn't valid anymore.

Steps to reproduce:

• Enable Ambient Occlusion in the Render Tab
• Switch viewport shading to Material or Render
• Switch Viewport Shading Render Pass to AO
• Disable Ambient Occlusion in the Render Tab

Expected results:

• As the viewport render pass option isn't available anymore it should select a good default (combined)

Steps from File:

• Disable Ambient Occlusion in the Render Tab
• Check the Viewport Shading Render Pass option

Same for the BLOOM pass