lua, PanelLayout - don't create a div if preamble is empty

Author: cderv

src/resources/filters/customnodes/panellayout.lua

@@ -76,7 +76,7 @@ _quarto.ast.add_handler({
         tbl.attributes = as_plain_table(tbl.attr.attributes)
         tbl.attr = nil
       end
-      tbl.preamble = pandoc.Div(tbl.preamble)
+      tbl.preamble = not _quarto.utils.is_empty_node(tbl.preamble) and pandoc.Div(tbl.preamble) or nil
     end
     -- compute vertical alignment and remove attribute
     if tbl.attributes == nil then

tests/docs/smoke-all/2025/01/31/11964.qmd

@@ -0,0 +1,25 @@
+---
+title: No empty preamble in layout panel
+format: 
+  html: default
+  typst:
+    keep-typ: true
+_quarto:
+  tests:
+    html:
+      ensureFileRegexMatches:
+        - [] 
+        - ['<div>\s*</div>\s*<div class="quarto-layout-panel"']
+    typst:
+      ensureTypstFileRegexMatches:
+        - []
+        - ['#block\[\s*\]']
+---
+
+:::{layout-ncol=2}
+
+Test 1
+
+Test 2
+
+:::