Fix an error on exit with C-d, and input y<RET>.

[fukamachi]

Fix to exit successfully.

CL-USER> ;; <C-d> here
Do you really want to exit ([y]/n)? y
attempt to THROW to a tag that does not exist: 0
 [Condition of type SIMPLE-CONTROL-ERROR]

Restarts:
 0: [*ABORT] Deduce debugger level.
 1: [*EXIT] Exit CL-REPL.
 2: [*RETRY] Try evaluating again.

Backtrace:
 0: (CL-REPL::EXIT-WITH-PROMPT)
 1: (CL-REPL::READ-INPUT)
 --more--

Usage:
  Ctrl+r: select restart. Ctrl+t: show backtrace.

[1]CL-USER>