OBJ Import: better handling for metallic

retrival of metallic (ab)uses OBJ material ambient term.
this can be non-zero, but in case of no reflections (OBJ 'illum' < 3)
metallic should be zero.

Fixes T60150

io_scene_obj/import_obj.py

@@ -219,6 +219,9 @@ def create_materials(filepath, relpath,
             if do_reflection:
                 if "metallic" not in context_material_vars:
                     context_mat_wrap.metallic = 1.0
+            else:
+                # since we are (ab)using ambient term for metallic (which can be non-zero)
+                context_mat_wrap.metallic = 0.0
 
             if do_transparency:
                 if "ior" not in context_material_vars: