fix: the vi-insert mode should insert the pending-keys (the length of command-keys > 1) for self-insert command.

[sakurawald]

To close issue: #1609

Before this commit: When executing the self-insert command in vi-insert mode, the first key in command-keys will be consumed, however, the rest keys in command-keys will be ignore.

After this commit: The rest keys in command-keys will also be inserted in vi-insert-mode.

This is useful when you define the j k as escape for vi-insert mode.

And you can press j k as escape in vi-insert-mode, and j e as self-insert j and self-insert e.