fix-missing-reference-asset-display

[Synyproxy]

Description

fix: display "(Missing Reference)" for missing asset references (#739)

Added an asset existence checker callback to the GUIHelpers system.
When an asset reference points to a non-existent file, AssetFields now
display the asset name with "(Missing Reference)" appended, making it
clear that the reference is invalid.

Related Issue(s)

(#739)
Fixes #(issue number)
739

Checklist

• My code follows the project's code style guidelines
• When applicable, I have commented my code, particularly in hard-to-understand areas
• When applicable, I have updated the documentation accordingly
• My changes don't generate new warnings or errors
• I have reviewed and take responsibility for all code in this PR (including any AI-assisted contributions)

[Gopmyc]

Naaaaa
You submit the PR right when I start working on it 😂

[Gopmyc]

Hey, quick note on your PR :
in GUIDrawer::GetAssetDisplayName, the (Missing Reference) logic looks like it’s placed after a return, so it’s currently unreachable.

I think the fix is just to restructure the function a bit, compute the stem first, then check for existence before the final return.

Also, to stay consistent with CONTRIBUTING.md, make sure to keep braces on if statements (F.4) and avoid one-liner ifs (F.5).