Fix viable next sibling search for replaceWith

Closes phpGH-11888.

Author: nielsdos

NEWS

@@ -30,6 +30,7 @@ PHP                                                                        NEWS
   . Fix manually calling __construct() on DOM classes. (nielsdos)
   . Fixed bug GH-11830 (ParentNode methods should perform their checks
     upfront). (nielsdos)
+  . Fix viable next sibling search for replaceWith. (nielsdos)
 
 - Core:
   . Fixed oss-fuzz #60741 (Leak in open_basedir). (ilutov)

ext/dom/tests/replaceWith_non_viable_next_sibling.phpt

@@ -0,0 +1,36 @@
+--TEST--
+replaceWith() with a non-viable next sibling
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+$doc = new DOMDocument;
+$doc->loadXML(<<<XML
+<?xml version="1.0"?>
+<container>
+    <child>
+        <alone/>
+    </child>
+</container>
+XML);
+
+$container = $doc->documentElement;
+$child = $container->firstElementChild;
+$alone = $child->firstElementChild;
+
+$child->after($alone);
+echo $doc->saveXML();
+$child->replaceWith($alone);
+echo $doc->saveXML();
+?>
+--EXPECT--
+<?xml version="1.0"?>
+<container>
+    <child>
+        
+    </child><alone/>
+</container>
+<?xml version="1.0"?>
+<container>
+    <alone/>
+</container>