Add the `Generate Lightmap UV2` check un `func_detail`'s

[Adrihfu]

Right now (version 2.2.11) when importing a func_detail with the property
import/generate_lightmap_uv2 set to false, the UV2 is been generated.

When imporing a vmf at runtime a Godot Error and GodotVMF Warning occurs:

ERROR: Parameter "array_mesh_lightmap_unwrap_callback" is null.
   at: lightmap_unwrap_cached (scene/resources/mesh.cpp:2084)
   GDScript backtrace (most recent call first):
       [0] _entity_setup (res://addons/godotvmf/entities/func_detail.gd:11)
       [1] _ready (res://addons/godotvmf/src/vmf_entity_node.gd:69)
       [2] push_entity_to_group (res://addons/godotvmf/src/vmf_node.gd:246)
       [3] import_entities (res://addons/godotvmf/src/vmf_node.gd:280)
       [4] _custom_import_map (res://src/main.gd:59)
       [5] _on_button_load_pressed (res://src/main.gd:25)

WARNING: [GodotVMF] func_detail 1132: lightmap_unwrap failed (3), skipping UV2
     at: push_warning (core/variant/variant_utility.cpp:1034)
     GDScript backtrace (most recent call first):
         [0] warn (res://addons/godotvmf/src/vmf_logger.gd:10)
         [1] _entity_setup (res://addons/godotvmf/entities/func_detail.gd:13)
         [2] _ready (res://addons/godotvmf/src/vmf_entity_node.gd:69)
         [3] push_entity_to_group (res://addons/godotvmf/src/vmf_node.gd:246)
         [4] import_entities (res://addons/godotvmf/src/vmf_node.gd:280)
         [5] _custom_import_map (res://src/main.gd:59)
         [6] _on_button_load_pressed (res://src/main.gd:25)

[H2xDev]

It should be fixed now. Please check.

[Adrihfu]

Works fine, Thank you.