Fix #137: Shape keys start with 1.0 value on PSK import

There was an undocumented change in 5.0 where the shape keys now start with a weight of 1.0 instead of 0.0 when created.

I have added an assert in the shape key test to make sure that the values are set to `0.0`.

This also fixes the assertion in the poll function (asserts should never be in poll functions).

io_scene_psk_psa/psa/import_/operators.py

@@ -13,7 +13,8 @@ from ..reader import PsaReader
 
 
 def psa_import_poll(cls, context: Context):
-    assert context.view_layer and context.view_layer.objects.active
+    if context.view_layer is None or context.view_layer.objects.active is None:
+        return False
     active_object = context.view_layer.objects.active
     if active_object is None or active_object.type != 'ARMATURE':
         cls.poll_message_set('The active object must be an armature')

io_scene_psk_psa/psk/importer.py

@@ -275,6 +275,7 @@ def import_psk(psk: Psk, context: Context, name: str, options: PskImportOptions)
 
             for morph_info in psk.morph_infos:
                 shape_key = mesh_object.shape_key_add(name=morph_info.name.decode('windows-1252'), from_mix=False)
+                shape_key.value = 0.0
 
                 for _ in range(morph_info.vertex_count):
                     morph_data = next(morph_data_iterator)