Fixes select mode for the Asset Browser to properly filter to the selecting type
Fixes the imageType in the asset import window inspector to properly set to the importing image asset's discovered type if valid
Fixes AssetBrowser asset selection return so it returns back a valid assetId
Fixes TerrainMaterial save crash by ensuring we fill in the diffuseMapAsset
Removes saving of TerrainMaterial being saved to a generic script file if one isn't found for an existing TerrainMaterialAssets