Fix #2691: keep image name suffixes like ".001" on export

[Builder106]

Fixes #2691.

Problem

On export, image datablock names containing a . (Blender's own duplicate suffix, e.g. Image.001, Image.Other.001) lose everything after the last dot. Distinct images then collapse to the same glTF image name (Image, Image), which is ambiguous and, as reported, scrambles image names on re-import.

Cause

In exp/material/image.py, __gather_name runs os.path.splitext(img.name) when combining names:

for img in imgs:
    name, extension = os.path.splitext(img.name)   # "Image.001" -> "Image"
    names.append(name)

img.name is a datablock name, not a filename, so splitext wrongly treats .001 / .Other.001 as a file extension. (The shared-filepath branch a few lines above is already correct — it only strips a whitelisted real image extension.)

Fix

Apply that same whitelist guard to the datablock-name loop: only strip a genuine image extension (.png / .jpg / .jpeg / .webp); otherwise keep the full name. This follows the guidance on the issue — "when possible, we need to do our best to export correctly the name, avoiding ambiguity."

Verification

Three images named Image, Image.001, Image.Other.001, each on its own plane, exported to GLB (Blender 5.x):

	images[].name in the GLB
before	["Image", "Image", "Image.Other"] (collision)
after	["Image", "Image.001", "Image.Other.001"]

Genuine file extensions are still stripped (wood.png → wood), and dotted names that are not extensions are preserved (v1.5_diffuse stays intact).