shader assignment fix

src/mol-gl/shader/chunks/color-assign-material.glsl

 #if defined(dColorType_uniform)
-    vec4 material.rgb = uColor;
+    vec4 material = vec4(uColor, 1.0);
 #elif defined(dColorType_attribute) || defined(dColorType_instance) || defined(dColorType_element) || defined(dColorType_elementInstance) || defined(dColorType_objectPicking) || defined(dColorType_instancePicking) || defined(dColorType_elementPicking)
     vec4 material = vColor;
 #endif
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