Fix for NPE when FieldFormalParameterElement references an unresolved field.

pkg/analysis_server/lib/src/computer/computer_navigation.dart

Index: pkg/analysis_server/lib/src/computer/computer_navigation.dart
diff --git a/pkg/analysis_server/lib/src/computer/computer_navigation.dart b/pkg/analysis_server/lib/src/computer/computer_navigation.dart
index bce017c7bceeef3ec02d74b5ec1a1c13d44ee5e5..a82cbe1e20c64fb4e0d509eeda59c372698d79c0 100644
--- a/pkg/analysis_server/lib/src/computer/computer_navigation.dart
+++ b/pkg/analysis_server/lib/src/computer/computer_navigation.dart
@@ -30,12 +30,12 @@ class DartUnitNavigationComputer {
   }
 
   void _addRegion(int offset, int length, Element element) {
-    if (element == null || element == DynamicElementImpl.instance) {
-      return;
-    }
     if (element is FieldFormalParameterElement) {
       element = (element as FieldFormalParameterElement).field;
     }
+    if (element == null || element == DynamicElementImpl.instance) {
+      return;
+    }
     protocol.Element target = new protocol.Element.fromEngine(element);
     _regions.add(new protocol.NavigationRegion(offset, length, [target]));
   }