MWSE ESS import fails with an SCPT size mismatch with >255 mods

Importing an MWSE save with >255 mods fails with an error:

Error: ESM Error: record size mismatch, requested 4, got 8
  File: E:\Games\Galaxy\Morrowind\Saves\MWSEImpo0001.ess
  Record: SCPT
  Subrecord: RNAM
  Offset: 0x124be

MWSE switches to a new 8-byte format for mod index and content file ID when the save exceeds Vanilla's 255 mod limit.

Steps to Reproduce

1. Install MWSE
2. Start a new game in Morrowind.exe with >255 mods and a mod past this limit that contains an active script.
3. Save the game
4. Attempt to import the save with OpenMW's ESS Importer

Example save with 8-byte format: TestMWSE0000.zip