Fix #1280: babashka REPL doesn't quit right after ctrl-d (#1450)

the problem is that parser/parse-next waits for an enter before returning an object
we can use peek-char to pre-emptively react to any EOF at the start of the line
in case of not-start-of-line, parse-next takes over

Co-authored-by: Alice Margatroid <code@alice.bunkerlabs.net>

src/babashka/impl/repl.clj

@@ -63,13 +63,14 @@
                   (eval-form sci-ctx `(apply require (quote ~m/repl-requires)))))
       :read (or read
                 (fn [_request-prompt request-exit]
-                  (let [v (parser/parse-next sci-ctx in)]
-                    (skip-if-eol in)
-                    (if (or (identical? :repl/quit v)
-                            (identical? :repl/exit v)
-                            (identical? parser/eof v))
-                      request-exit
-                      v))))
+                  (if (nil? (r/peek-char in))
+                    request-exit
+                    (let [v (parser/parse-next sci-ctx in)]
+                      (skip-if-eol in)
+                      (if (or (identical? :repl/quit v)
+                              (identical? :repl/exit v))
+                        request-exit
+                        v)))))
       :eval (or eval
                 (fn [expr]
                   (sci/with-bindings {sci/file "<repl>"