BPackageInfoSet::Iterator: Fix NULL pointer dereference

Since the BPackageInfoSet's map is created lazily, it can be NULL when
an Iterator is constructed.

headers/os/package/PackageInfoSet.h

@@ -49,8 +49,7 @@ private:
 
 class BPackageInfoSet::Iterator {
 public:
-								Iterator();
+								Iterator(const PackageMap* map = NULL);
-								Iterator(const PackageMap* map);
 
 			bool				HasNext() const;
 			const BPackageInfo*	Next();

src/kits/package/PackageInfoSet.cpp

@@ -173,18 +173,10 @@ private:
 // #pragma mark - Iterator
 
 
-BPackageInfoSet::Iterator::Iterator()
-	:
-	fMap(NULL),
-	fNextInfo(NULL)
-{
-}
-
-
 BPackageInfoSet::Iterator::Iterator(const PackageMap* map)
 	:
 	fMap(map),
-	fNextInfo(map->GetIterator().Next())
+	fNextInfo(map != NULL ? map->GetIterator().Next() : NULL)
 {
 }