fix (keymaps): Prevent key press cancellation when no completions available

[hugovntr]

Description

With the current keymaps setup, pressing the accept/dismiss key (e.g <Tab>, <S-Tab>) does not have any effect if there are no completion suggestions available. This effectively "cancels" the keypress and can be confusing/annoying for users.

For example, in inset mode, when using <Tab> as the accept key, if no completions are available, the tab key becomes inactive.

This PR addresses this issue by ensuring that pressing the accept/dismiss key always falls back to the original keypress when there are no completions

Changes

• keymaps — Modified accept_suggestion and dismiss_suggestion functions to fallback to the original keypress when no completions exists.
• keymaps — Same functions as above. Ensured that completion could not be accepted unless shown to the user.

[ViViDboarder]

Oh, just found this as an alternative to the PR I just submitted #123, both fix #61.