fixes #21290; deindent if the last same level is a text node (#21293)

* fixes #21290; deindent if the last same level is a text node

* add one more test

tests/stdlib/txmltree.nim

@@ -1,4 +1,4 @@
-import std/[xmltree, assertions]
+import std/[xmltree, assertions, xmlparser]
 
 
 block:
@@ -83,3 +83,19 @@ block:
   x.add newElement("sonTag")
   x.add newEntity("my entity")
   doAssert $x == "<myTag>my text<sonTag />&my entity;</myTag>"
+
+block: # bug #21290
+  let x = newXmlTree("foo",[
+    newXmlTree("bar",[
+      newText("Hola"),
+      newXmlTree("qux",[
+        newXmlTree("plugh",[])
+      ])
+    ])
+  ])
+
+  let s = $x
+  doAssert $parseXml(s) == s
+  doAssert s == """<foo>
+  <bar>Hola<qux>    <plugh />  </qux></bar>
+</foo>"""