Fix internal constructor in context.

BUG=
R=lrn@google.com

Review URL: https://codereview.chromium.org//434393002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/path@38845 260f80e4-7a28-3924-810f-c04153c831b5
diff --git a/lib/src/context.dart b/lib/src/context.dart
index 8901049..7a88909 100644
--- a/lib/src/context.dart
+++ b/lib/src/context.dart
@@ -44,7 +44,7 @@
   }
 
   /// Create a [Context] to be used internally within path.
-  Context._internal() : style = Style.platform;
+  Context._internal() : style = Style.platform, _current = null;
 
   Context._(this.style, this._current);