fix(api): make open_win/win_set_config check if splitting allowed

Problem: splitting is disallowed in some cases to prevent the window layout
changes while a window is closing, but it's not checked for.

Solution: check for this, and set the API error message directly.

(Also sneak in a change to tui.c that got lost from #27352; it's a char* buf,
and the memset is assuming one byte each anyway)

1 files changed, 8 insertions, 0 deletions

diff --git a/src/nvim/api/win_config.c b/src/nvim/api/win_config.c
index 3959e74af9..557c2f37f9 100644
--- a/src/nvim/api/win_config.c
+++ b/src/nvim/api/win_config.c
@@ -246,6 +246,10 @@ Window nvim_open_win(Buffer buffer, Boolean enter, Dict(win_config) *config, Err
       }
     }
 
+    if (!check_split_disallowed_err(parent ? parent : curwin, err)) {
+      return 0;  // error already set
+    }
+
     if (HAS_KEY_X(config, vertical) && !HAS_KEY_X(config, split)) {
       if (config->vertical) {
         fconfig.split = p_spr ? kWinSplitRight : kWinSplitLeft;
@@ -440,6 +444,10 @@ void nvim_win_set_config(Window window, Dict(win_config) *config, Error *err)
       return;
     }
 
+    if (!check_split_disallowed_err(win, err)) {
+      return;  // error already set
+    }
+
     if (was_split) {
       win_T *new_curwin = NULL;