Lenient URI template encoding

URI template encoding ignores mismatched curly braces, treating them as
literal parts instead.

Issue: SPR-17630

spring-web/src/test/java/org/springframework/web/util/UriComponentsTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -131,6 +131,12 @@ public class UriComponentsTests {
 		assertEquals("/myurl/test/show", uriComponents.getPath());
 	}
 
+	@Test // SPR-17630
+	public void uirTemplateExpandWithMismatchedCurlyBraces() {
+		assertEquals("/myurl/?q=%7B%7B%7B%7B",
+				UriComponentsBuilder.fromUriString("/myurl/?q={{{{").encode().build().toUriString());
+	}
+
 	@Test // SPR-12123
 	public void port() {
 		UriComponents uri1 = fromUriString("http://example.com:8080/bar").build();