fix(extmarks): crash with sign after many marks

fixes #27137

src/nvim/marktree.c

@@ -1576,7 +1576,9 @@ bool marktree_itr_step_out_filter(MarkTree *b, MarkTreeIter *itr, MetaFilter met
     }
 
     itr->i = itr->x->n;
-    marktree_itr_next(b, itr);  // no filter, just reuse the code for step to parent
+
+    // no filter needed, just reuse the code path for step to parent
+    marktree_itr_next_skip(b, itr, true, false, NULL, NULL);
   }
 
   return itr->x;

test/functional/ui/decorations_spec.lua

@@ -4548,6 +4548,7 @@ describe('decorations: signs', function()
       [1] = {foreground = Screen.colors.Blue4, background = Screen.colors.Grey};
       [2] = {foreground = Screen.colors.Blue1, bold = true};
       [3] = {background = Screen.colors.Yellow1, foreground = Screen.colors.Blue1};
+      [4] = {foreground = Screen.colors.Gray100, background = Screen.colors.Red};
     }
 
     ns = api.nvim_create_namespace 'test'
@@ -5021,6 +5022,21 @@ l5
                           |
     ]]}
   end)
+
+  it('no crash with sign after many marks #27137', function()
+    screen:try_resize(20, 4)
+    insert('a')
+    for _ = 0, 104 do
+      api.nvim_buf_set_extmark(0, ns, 0, 0, {hl_group = 'Error', end_col = 1})
+    end
+    api.nvim_buf_set_extmark(0, ns, 0, 0, {sign_text = 'S1'})
+
+    screen:expect{grid=[[
+      S1{4:^a}                 |
+      {2:~                   }|*2
+                          |
+    ]]}
+  end)
 end)
 
 describe('decorations: virt_text', function()