This affects CSI sequences that aren't explicitly bound but arrive
within the usual KEYTIMEOUT time limits. A single undefined-key widget
is run instead of unintended bindings for Escape and other characters in
the sequence.
Seen with magic-space.
If there's a parse error in command subtitution we need to complete
reading history to ensure the command line buffer is finished.
This makes it work even if the self-insert applies to a sequence longer
than an initial byte, including the case of a complete binding to a full
character sequence.
