Unable to paste chain from clipboard after clear canvas action

[AlexeyGirin]

Steps to Reproduce

1. Go to Macro - Sequence mode (clean canvas)
2. Load from HELM: RNA1{R(U)P.R(U)}|RNA2{R(A)P.R(A)}$RNA2,RNA1,5:pair-2:pair$$$V2.0
   
3. Click between A symbols to switch to Edit mode
   
4. Press Clear Canvas button
5. Paste any HELM from clipboard to canvas (RNA1{R(U)P.R(U)}|RNA2{R(A)P.R(A)}$RNA2,RNA1,5:pair-2:pair$$$V2.0 in my case)

Actual behavior
System throws an error: Convert error! Given string could not be loaded as (query or plain) molecule or reaction, see the error messages: 'molecule auto loader: SMILES loader: 'a' specifier is allowed only for query molecules', 'scanner: BufferScanner::read() error', 'SEQUENCE loader: Unknown polymer type 'PASTE'.', 'molecule auto loader: SMILES loader: invalid character within atom description: 't''

OR
System throws an error: Paste of several fragments is prohibited in text-editing mode.

Expected behavior
No errors or exceptions

Versions

• Ketcher Version 3.1.0-rc.2 Build at 2025-02-07; 15:09:23
• Indigo Version 1.29.0-rc.1.0-g2e30df8f7-wasm32-wasm-clang-19.0.0
• Chrome Version 133.0.6943.54 (Official Build) (64-bit)
• Win10

Issue found while testing: #5942