define a default value for the auto-fit setting

Fixes an issue where migrating the pref to default=ON didn't take effect
until you visited general preferences.

Change-Id: Ie86713da8da5aed0382c1bb7fc33247fccef8b23
diff --git a/src/com/android/mail/ui/ConversationViewFragment.java b/src/com/android/mail/ui/ConversationViewFragment.java
index 10f32b3..7bed51b 100644
--- a/src/com/android/mail/ui/ConversationViewFragment.java
+++ b/src/com/android/mail/ui/ConversationViewFragment.java
@@ -1037,7 +1037,7 @@
     }
 
     private static boolean isOverviewMode(Account acct) {
-        return acct.settings.conversationViewMode == UIProvider.ConversationViewMode.OVERVIEW;
+        return acct.settings.isOverviewMode();
     }
 
     private void setupOverviewMode() {