Fix T102810: Error for import FBX ASCII

The import script was broken in rBA27ee43296585, because I forgot an
import for i18n. ASCII FBX is still not supported, but at least the
erro reporting won't crash.

Reported by Evan Wilson in D16373.

io_scene_fbx/import_fbx.py

@@ -15,6 +15,7 @@ if "bpy" in locals():
         importlib.reload(fbx_utils)
 
 import bpy
+from bpy.app.translations import pgettext_tip as tip_
 from mathutils import Matrix, Euler, Vector
 
 # -----