added to apps.dashboard.views, share_list() FBV, a try/except catch that accounts for nonexistent users; .test.test_views ensures functionality

src/apps/dashboard/views.py

@@ -40,6 +40,9 @@ def my_lists(request, user_id):
 
 def share_list(request, list_id):
     our_list = List.objects.get(id=list_id)
-    recipient = User.objects.get(email=request.POST["recipient"])
-    our_list.shared_with.add(recipient)
+    try:
+        recipient = User.objects.get(email=request.POST["recipient"])
+        our_list.shared_with.add(recipient)
+    except User.DoesNotExist:
+        pass
     return redirect(our_list)