Fix bug with intentional trailing spaces in instruct template prefix

[netrunnereve]

Checklist:

• [x] I have read the Contributing guidelines.

If we have an intentional trailing space in an instruct template prefix (e.g. '[INST] ' + message['content'] + ' [/INST]') it gets stripped out during impersonation and we end up with something like [INST]<impersonated message>. However when I press generate it gets corrected back into [INST] <impersonated message>, which causes the backend to reprocess all the impersonated text.