Fix the PkgFileIterator Constructor which defaults to the wrong value.

(0 instead of the HeaderP) This breaks the Cache Validation functionality
as the end() doesn't test for NULL.
(The fault was introduced with the rewriting of the CacheIterators)

apt-pkg/cacheiterators.h

@@ -345,7 +345,8 @@ class pkgCache::PkgFileIterator : public Iterator<PackageFile, PkgFileIterator>
 
 	// Constructors
 	inline PkgFileIterator() : Iterator<PackageFile, PkgFileIterator>() {};
-	inline PkgFileIterator(pkgCache &Owner,PackageFile *Trg = 0) : Iterator<PackageFile, PkgFileIterator>(Owner, Trg) {};
+	inline PkgFileIterator(pkgCache &Owner) : Iterator<PackageFile, PkgFileIterator>(Owner, Owner.PkgFileP) {};
+	inline PkgFileIterator(pkgCache &Owner,PackageFile *Trg) : Iterator<PackageFile, PkgFileIterator>(Owner, Trg) {};
 };
 									/*}}}*/
 // Version File								/*{{{*/