Update XPathParser#get_first and XPathParser#predicate to both setup document

Author: tompng

lib/rexml/xpath_parser.rb

@@ -88,12 +88,12 @@ def parse path, node
         node = node.first
       end
 
-      @document = node.document
       match(path_stack, node)
     end
 
     def get_first path, node
       path_stack = @parser.parse( path )
+      @document = node.document
       first( path_stack, node )
     end
 
@@ -149,6 +149,7 @@ def first( path_stack, node )
 
 
     def match(path_stack, node)
+      @document = node.document
       nodeset = [node]
       result = expr(path_stack, nodeset)
       case result