Fix Unity material color dump guard

[fc470505146]

Summary

Fix Unity SDK hierarchy dump when a Renderer material does not expose the _Color shader property.

This patch updates both Unity3D/ugui/UnityNode.cs and Unity3D/uguiWithTMPro/UnityNode.cs to:

• use the local render variable returned by gameObject.GetComponent<Renderer>()
• guard material.color access with material.HasProperty("_Color")

Root cause

Material.color internally reads the _Color shader property. Some shaders, such as TextMeshPro/Mobile/Distance Field, do not define _Color. During Poco hierarchy dump this can emit Unity errors like:

Material 'LiberationSans SDF Material (Instance)' with Shader 'TextMeshPro/Mobile/Distance Field' doesn't have a color property '_Color'
UnityEngine.Material:get_color ()
Poco.UnityNode:GetImageSourceTexture ()

The current code also creates a local variable named render, but then checks and reads the field renderer instead.

Impact

For materials with _Color, behavior is unchanged. For materials without _Color, Poco now skips the texture/color payload instead of triggering Unity errors while dumping the hierarchy.

Validation

Validated the same change in a Unity 6000.1.12f1 project using Poco Unity SDK and TextMeshPro UI. Before the patch, entering gameplay and dumping UI nodes triggered repeated _Color errors. After the patch, Poco can dump and interact with the UI, and a test GM flow completed successfully:

connected
PlayButton exists: True
SettingButton ready: True
GMForceSuccess: ok
LandedUI exists: True
NextButton exists: True