Null check cursor

Mock provider is returning null on this query in testing.

b/12085240

Change-Id: Ifa5edc03707a6050acdbd5184a44409d46004e7e
diff --git a/src/com/android/email2/ui/MailActivityEmail.java b/src/com/android/email2/ui/MailActivityEmail.java
index 8868c04..bf78ce4 100644
--- a/src/com/android/email2/ui/MailActivityEmail.java
+++ b/src/com/android/email2/ui/MailActivityEmail.java
@@ -115,7 +115,7 @@
                     Account.CONTENT_URI,
                     Account.ID_PROJECTION,
                     null, null, null);
-            boolean enable = c.getCount() > 0;
+            boolean enable = c != null && c.getCount() > 0;
             setServicesEnabled(context, enable);
             return enable;
         } finally {