System shows molecular mass and molecular formula even if few chains on the canvas

[AlexeyGirin]

Steps to Reproduce

1. Go to Macromolecules mode - Flex canvas (empty)
2. Load from KET (unzip first): System shows molecular mass and molecular formula even if few chains on the canvas.zip
   
3. Open Calculate properties (press Alt+C)

Actual behavior
System shows molecular mass and molecular formula

Expected behavior
System doesn't show molecular mass and molecular formula

As per requirement:

5. If the "Calculate Properties" window is opened and no selection is made when there is more than one chain on canvas, values in the "Calculate Properties" window should be blank and grayed out, and the window should contain an error message: "Select monomer, chain or part of a chain".

Environment details:

• Ketcher Version 3.4.0-rc.3 Build at 2025-05-15; 19:51:50
• Indigo Version 1.32.0-rc.2.0-g94ab270bd-wasm32-wasm-clang-19.0.0
• Chrome Version 136.0.7103.93 (Official Build) (64-bit)
• Win10

Found while testing: #5727

[SefaBilgii]

This issue is reproducible

Ketcher Version: 3.6.0-rc.1
OS: MacOs Sequoia Version 15.5
Browser : Chrome Version 138.0.7204.169