Fix a bug in (read-string) which affects non-special characters.

src/reader.rls

@@ -275,7 +275,9 @@
                         (next-char)
                         (cdr item))])]
               [else 
-                 current-char]))
+                 (let ([ch current-char])
+                   (next-char)
+                   ch)]))
 
           (let ([ch (read-one-char)])
             (if ch