New name UI_UPDATE for interpret_move's return "".

Now midend.c directly tests the returned pointer for equality to this
value, instead of checking whether it's the empty string.

A minor effect of this is that games may now return a dynamically
allocated empty string from interpret_move() and treat it as just
another legal move description. But I don't expect anyone to be
perverse enough to actually do that! The main purpose is that it
avoids returning a string literal from a function whose return type is
a pointer to _non-const_ char, i.e. we are now one step closer to
being able to make this code base clean under -Wwrite-strings.

1 files changed, 2 insertions, 2 deletions

diff --git a/range.c b/range.c
index 4dd39b9..8017f8d 100644
--- a/range.c
+++ b/range.c
@@ -1360,14 +1360,14 @@ static char *interpret_move(const game_state *state, game_ui *ui,
                 else if (do_post)
                     return nfmtstr(40, "W,%d,%d", ui->r, ui->c);
                 else
-                    return "";
+                    return UI_UPDATE;
 
             } else if (!out_of_bounds(ui->r + dr[i], ui->c + dc[i], w, h)) {
                 ui->r += dr[i];
                 ui->c += dc[i];
             }
         } else ui->cursor_show = TRUE;
-        return "";
+        return UI_UPDATE;
     }
 
     if (action == hint) {