encoding.xml: fix parsing of single letter tag names (#19815)

vlib/encoding/xml/parser.v

@@ -534,9 +534,12 @@ fn parse_single_node(first_char u8, mut reader io.Reader) !XMLNode {
 	if ch == `/` {
 		return error('XML node cannot start with "</".')
 	}
-	contents.write_u8(ch)
 
-	for {
+	if ch != `>` {
+		contents.write_u8(ch)
+	}
+
+	for ch != `>` {
 		ch = next_char(mut reader, mut local_buf)!
 		if ch == `>` {
 			break
@@ -547,7 +550,7 @@ fn parse_single_node(first_char u8, mut reader io.Reader) !XMLNode {
 	tag_contents := contents.str().trim_space()
 
 	parts := tag_contents.split_any(' \t\n')
-	name := first_char.ascii_str() + parts[0]
+	name := if parts.len > 0 { first_char.ascii_str() + parts[0] } else { first_char.ascii_str() }
 
 	// Check if it is a self-closing tag
 	if tag_contents.ends_with('/') {

vlib/encoding/xml/test/local/18_single_letter_tag/shared.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<sst count="5" uniqueCount="5">
+  <si>
+    <t>Item 1</t>
+  </si>
+  <si>
+    <t>Item 2</t>
+  </si>
+  <si>
+    <t>Item 3</t>
+  </si>
+  <si>
+    <t>Item 4</t>
+  </si>
+  <si>
+    <t>Item 5</t>
+  </si>
+</sst>

vlib/encoding/xml/test/local/18_single_letter_tag/shared_test.v

@@ -0,0 +1,68 @@
+module main
+
+import os
+import encoding.xml
+
+fn test_valid_parsing() {
+	path := os.join_path(os.dir(@FILE), 'shared.xml')
+
+	expected := xml.XMLDocument{
+		root: xml.XMLNode{
+			name: 'sst'
+			attributes: {
+				'count':       '5'
+				'uniqueCount': '5'
+			}
+			children: [
+				xml.XMLNode{
+					name: 'si'
+					children: [
+						xml.XMLNode{
+							name: 't'
+							children: ['Item 1']
+						},
+					]
+				},
+				xml.XMLNode{
+					name: 'si'
+					children: [
+						xml.XMLNode{
+							name: 't'
+							children: ['Item 2']
+						},
+					]
+				},
+				xml.XMLNode{
+					name: 'si'
+					children: [
+						xml.XMLNode{
+							name: 't'
+							children: ['Item 3']
+						},
+					]
+				},
+				xml.XMLNode{
+					name: 'si'
+					children: [
+						xml.XMLNode{
+							name: 't'
+							children: ['Item 4']
+						},
+					]
+				},
+				xml.XMLNode{
+					name: 'si'
+					children: [
+						xml.XMLNode{
+							name: 't'
+							children: ['Item 5']
+						},
+					]
+				},
+			]
+		}
+	}
+	actual := xml.XMLDocument.from_file(path)!
+
+	assert expected == actual, 'Parsed XML document should be equal to expected XML document'
+}