Shape Key export fails when the mesh is in Edit Mode

The simple work-around is to switch to Object mode before exporting, but it did cause me some head-aches. When the export of a mesh with shape keys is done in Edit Mode, the vertex positions for all the shape keys are identical.

[shape_key_export_bug.zip](https://github.com/godotengine/collada-exporter/files/2615465/shape_key_export_bug.zip)

1) Start Blender 2.79b, Load "PyramidShapes.blend".
2) Export a first time to see the Pyramid with the correct blend shapes in Godot.
3) In Blender, enter Edit Mode for the Pyramid.
4) Export a second time, open the COLLADA document in Godot: the shape keys are present, but there is no movement of vertices.

Start with the attached shape_key_export_bug.zip and reproduce the steps using Blender 2.79b and PyramidShapes.blend. Compare the COLLADA exports made in Object Mode and Edit Mode, then open them in Godot to verify that shape-key vertex positions still produce movement when exported from Edit Mode.

Written by the indexing model from the issue text.