Allow Bulk Upload to initialise on --- Bulk Upload All --- option

[AtlasLinden]

When uploading a GLTF model with multiple materials, the Bulk Upload dialog shows a drop down that initialises on the first material.

It would be beneficial to have this drop down initialise on the --- Bulk Upload All --- option.

Test Plan

Upload GLTF model with multiple materials and observe Bulk Upload dialog

[AtlasLinden]

Passed QA.
Verified on Second Life Project 7.1.14.15361077240 (GLTF Mesh Import) on Win11/MacOS