Fix T57055: Import wavefront OBJ does not correctly parse the '-bm' parameter.

Dummy typo, investigation done by @JimG, thanks!

io_scene_obj/__init__.py

@@ -21,7 +21,7 @@
 bl_info = {
     "name": "Wavefront OBJ format",
     "author": "Campbell Barton, Bastien Montagne",
-    "version": (2, 3, 6),
+    "version": (2, 3, 7),
     "blender": (2, 78, 0),
     "location": "File > Import-Export",
     "description": "Import-Export OBJ, Import OBJ mesh, UV's, materials and textures",

io_scene_obj/import_obj.py

@@ -177,7 +177,7 @@ def create_materials(filepath, relpath,
 
         elif type == 'Bump':
             bump_mult = map_options.get(b'-bm')
-            bump_mult = float(bump_mult[0]) if (bump_mult is not None and len(bump_mult) > 1) else 1.0
+            bump_mult = float(bump_mult[0]) if (bump_mult and len(bump_mult[0]) > 1) else 1.0
 
             if use_cycles:
                 mat_wrap.normal_image_set(image)