Bug when copy-pasting blocks from removed text extensions

[ScrTwPm]

Steps:

1. Load a custom text unsandboxed extension - I do this a lot while making extensions and others may too unless they use localhost HTTP server.

2. Use a block from it in a script and copy the script (right click -> Ctrl + C)

3. Remove the extension (right click -> Remove extension)

4. Paste the script (Ctrl + V)

5. Try to run it

The editor will throw an error

It will say there is an unknown block.

This is probably something that would rarely happen because people likely won't delete extensions after using them but it is a bug that can probably be fixed.