patch 9.0.1599: Cursor not adjusted when 'splitkeep' is not "cursor"

Problem:    Cursor not adjusted when near top or bottom of window and
            'splitkeep' is not "cursor".
Solution:   Move boundary checks to outer cursor move functions, inner
            functions should only return valid cursor positions. (Luuk van
            Baal, closes #12480)
diff --git a/src/proto/edit.pro b/src/proto/edit.pro
index 4513f4f..f918528 100644
--- a/src/proto/edit.pro
+++ b/src/proto/edit.pro
@@ -19,9 +19,9 @@
 void beginline(int flags);
 int oneright(void);
 int oneleft(void);
-linenr_T cursor_up_inner(win_T *wp, long n);
+void cursor_up_inner(win_T *wp, long n);
 int cursor_up(long n, int upd_topline);
-linenr_T cursor_down_inner(win_T *wp, long n);
+void cursor_down_inner(win_T *wp, long n);
 int cursor_down(long n, int upd_topline);
 int stuff_inserted(int c, long count, int no_esc);
 char_u *get_last_insert(void);