[libxml2] Fix comparison of nodesets to strings

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 5af594d8bc55121ae454cba4d05793d1db7ff612
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Sat Oct 7 14:54:45 2017 +0200

    Fix comparison of nodesets to strings
    
    Fix two bugs in xmlXPathNodeValHash which could lead to errors when
    comparing nodesets to strings:
    
    - Only use contents of text nodes to compute the hash for element nodes.
      Comments, PIs, and other node types don't affect the string-value and
      must be ignored.
    - Reset `string` to NULL for node types other than text.
    
    Reported by Aleksei on the mailing list:
    
        https://mail.gnome.org/archives/xml/2017-September/msg00016.html

 result/XPath/tests/strbase |   13 +++++++++++++
 test/XPath/docs/str        |    2 ++
 test/XPath/tests/strbase   |    1 +
 xpath.c                    |    6 +-----
 4 files changed, 17 insertions(+), 5 deletions(-)
---
diff --git a/result/XPath/tests/strbase b/result/XPath/tests/strbase
new file mode 100644
index 0000000..e6035ca
--- /dev/null
+++ b/result/XPath/tests/strbase
@@ -0,0 +1,13 @@
+
+========================
+Expression: //p[.='abc']
+Object is a Node Set :
+Set contains 2 nodes:
+1  ELEMENT p
+    ATTRIBUTE id
+      TEXT
+        content=1
+2  ELEMENT p
+    ATTRIBUTE id
+      TEXT
+        content=2
diff --git a/test/XPath/docs/str b/test/XPath/docs/str
index 547e54d..449de01 100644
--- a/test/XPath/docs/str
+++ b/test/XPath/docs/str
@@ -6,4 +6,6 @@
   <p><p>a span</p>n<p>ing one</p></p>
   <p><p>and an unbal</p><empty/>anced test</p>
   <p>for empty string <seq>123</seq></p>
+  <p id="1">a<b>b</b>c</p>
+  <p id="2"><!--X-->abc</p>
 </chapter>
diff --git a/test/XPath/tests/strbase b/test/XPath/tests/strbase
new file mode 100644
index 0000000..b818325
--- /dev/null
+++ b/test/XPath/tests/strbase
@@ -0,0 +1 @@
+//p[.='abc']
diff --git a/xpath.c b/xpath.c
index b816bd3..55432c7 100644
--- a/xpath.c
+++ b/xpath.c
@@ -6400,16 +6400,12 @@ xmlXPathNodeValHash(xmlNodePtr node) {
     }
     while (tmp != NULL) {
        switch (tmp->type) {
-           case XML_COMMENT_NODE:
-           case XML_PI_NODE:
            case XML_CDATA_SECTION_NODE:
            case XML_TEXT_NODE:
                string = tmp->content;
                break;
-           case XML_NAMESPACE_DECL:
-               string = ((xmlNsPtr)tmp)->href;
-               break;
            default:
+                string = NULL;
                break;
        }
        if ((string != NULL) && (string[0] != 0)) {