Can't render fragments with multiple external connections

[jblack-mestre]

Summary
When you try to render a fragment from a CDXML file with more than 1 external connection, indigo will not render any of the connections.

Steps to Reproduce

1. indigo-depict.exe multiple_external_connections.cdr multiple_external_connections.svg

Actual behavior
The bonds are missing between the alkane group and the OH functional groups. As a side effect, OH is turned into H2O.

(The C10H20 fragment is displaced due to a different bug #2747)

Expected behavior
Bonds are drawn between OH-C10H20-OH, as in chemdraw:

Environment details:

• windows 11
• indigo c037ec2

Attachments
multiple_external_connections.cdr.txt

Additional context
MoleculeCdxmlLoader::_parseCollections and MoleculeCdxmlLoader::_checkFragmentConnection are only coded to handle a single external connection for each fragment (possibly because it is becomes ambiguous to assign a set of external connections to a set of bonds).

[AlexeyGirin]

Verified.
Follow up issue created: epam/ketcher#6851

• Ketcher Version 3.3.0-rc.1 Build at 2025-04-02; 09:36:56
• Indigo Version 1.31.0-rc.1.0-g859747ec7-wasm32-wasm-clang-19.0.0
• Chrome Version 135.0.7049.42 (Official Build) (64-bit)
• Win10