fix(folds): error when deleting lines at end of buffer #35396

Problem:
with `foldmethod=expr foldexpr=v:lua.vim.treesitter.foldexpr()
foldminlines=0`, deleting lines at the end of the buffer always
reports an invalid top error, because the top value (i.e. the
start line number of the deletion) is always 1 greater than
the total line number of the modified buffer.

Solution:
remove the ml_line_count validation

src/nvim/lua/stdlib.c

@@ -563,7 +563,7 @@ static int nlua_foldupdate(lua_State *lstate)
   }
   // input is zero-based end-exclusive range
   linenr_T top = (linenr_T)luaL_checkinteger(lstate, 2) + 1;
-  if (top < 1 || top > win->w_buffer->b_ml.ml_line_count) {
+  if (top < 1) {
     return luaL_error(lstate, "invalid top");
   }
   linenr_T bot = (linenr_T)luaL_checkinteger(lstate, 3);

test/functional/treesitter/fold_spec.lua

@@ -832,4 +832,16 @@ t2]])
     command('set ft=c')
     eq(foldlevels, get_fold_levels())
   end)
+
+  it('no error when deleting lines at end of buffer with fml=0', function()
+    local screen = Screen.new(40, 2)
+    insert('hello')
+    parse('markdown')
+    command('set foldmethod=expr foldexpr=v:lua.vim.treesitter.foldexpr() foldminlines=0')
+    feed('o<Esc>dd')
+    screen:expect([[
+      ^hello                                   |
+                                              |
+    ]])
+  end)
 end)