Allow import with zip input on v1.2026.0 to v1.2026.8

Describe the bug

To follow:

• https://forum.plantuml.net/20479/problem-with-import-in-v1-2026-0

Version : v1.2026.0 to v1.2026.8

With PlantUML v1.2026.0 and later, I would like to import a ZIP file and load the .iuml files inside it by specifying their relative paths

I tested this with version v1.2026.8, but there was no change in the error. The same error occurs in v1.2026.0 and v1.2026.7. [...] The import itself does not fail; rather, the include fails after the import has completed. "Cannot include zip_inner_folder/zip_inner_file.iuml"

I have confirmed that zip_inner_folder/zip_inner_file.iuml inside some_file.zip does not contain @startuml and @enduml. Also, I confirmed that if I unzip some_file.zip instead of using !import, and then include zip_inner_folder/zip_inner_file.iuml directly, no error occurs.

• Could you please look into this issue? Thank you for your help.

To Reproduce

@startuml
!import some_file.zip
!include zip_inner_folder/zip_inner_file.iuml
@enduml

Expected behavior

• Allow import with zip input.

Regards, Th.