Read int from uvwsrc

Previously was reading a uint, which always failed. Since the output was never checked, this
seemed to work, and works fine for most models since they only use UV channel 0.

code/AssetLib/glTF2/glTF2Exporter.cpp

@@ -559,7 +559,11 @@ void glTF2Exporter::GetMatTex(const aiMaterial &mat, Ref<Texture> &texture, unsi
     aiString tex;
 
     // Read texcoord (UV map index)
-    mat.Get(AI_MATKEY_UVWSRC(tt, slot), texCoord);
+    // Note: must be an int to be successful.
+    int tmp = 0;
+    const auto ok = mat.Get(AI_MATKEY_UVWSRC(tt, slot), tmp);
+    if (ok == aiReturn_SUCCESS) texCoord = tmp;
+
 
     if (mat.Get(AI_MATKEY_TEXTURE(tt, slot), tex) == AI_SUCCESS) {
         std::string path = tex.C_Str();