Bugfix: yet another init problem after swapping contents

yeah, working with open fire is dangerous...

For performace reasons I've undercut the premise
to make GenNode / Record immutable. Now I'm dealing with
raw storage layout together with this quite hairy distinction
between "attribute scope" and "child scope"

In hindsight, it might have been better to implement Record
as a single list, and to maintain a shortcut pointer to jump
to the start of the attributes.

src/lib/diff/record-content-mutator.hpp

@@ -30,7 +30,10 @@
  ** details of doing so are highly coupled to the actual storage implementation
  ** of #Record, as well as to the actual procedure to apply a diff message, as
  ** implemented in lib::diff::DiffApplicationStrategy.
- ** 
+ ** @warning this struct is marked "internal" for a reason;
+ **          it serves the purpose to remove technicalities from usage site,
+ **          yet it is \em not a proper abstraction. Be sure you understand
+ **          the storage layout, especially when testing for iteration end.
  ** @see generic-record-update-test.cpp
  ** @see tree-diff-application-test.cpp
  ** @see Record::Mutator
@@ -115,6 +118,15 @@ namespace diff{
       
       void
       resetPos()
+        {
+          if (attribs.empty())
+            jumpToChildScope();
+          else
+            jumpToAttribScope();
+        }
+      
+      void
+      jumpToAttribScope()
         {
           pos = attribs.begin();
         }

src/lib/diff/tree-diff-application.hpp

@@ -108,6 +108,7 @@ namespace diff{
           void init()
             {
               target.swapContent (content);
+              content.resetPos();
             }
         };