[2D] [PSD Importer] PSB is not updated properly when moving from 2019.3.x with PSD Importer v.2.1.0 to 2019.4.x with PSD Importer v.2.1.5

Steps to Repro:

- download and unzip the attachment PentaquinOne_Backup_PSB MetaFiles Manifest_201109.zip
- create a new project in 2019.3.x and install PSD Importer v.2.1.0
- open the folder PSB-Models+Metas_2019.3 from the unzipped attachment
- copy the files Bandit_Archer.psb and Bandit_Archer.psb.meta into the new project; note that warnings appear:

File's Layer ID is not unique. Please report to developer. 0 Left_Leg_Upper::Left_Leg_Lower

- view the .psb in the sprite editor and skinning editor and note the size of the head sprite
- close the editor and reopen the project in 2019.4.x; note that warnings appear:

Layer Left_Leg_Lower: LayerId is not unique. Mapping will be done by Layer's name.
UnityEditor.Experimental.AssetImporters.ScriptedImporter:GenerateAssetData(AssetImportContext) (at /Users/bokken/buildslave/unity/build/Modules/AssetPipelineEditor/Public/ScriptedImporter.cs:22)

- view the .psb file in the sprite editor and skinning editor

Expected Result: The .psb appears the same as before upgrading
Actual Result: The head sprite slicing has changed which results in the character's head getting cut off in the skinning editor (refer to attached Before and After pics)