Let unencrypted messages through.

src/org/thoughtcrime/securesms/service/SmsListener.java

@@ -109,7 +109,7 @@ public class SmsListener extends BroadcastReceiver {
       return false;
     }
 
-    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.KITKAT &&
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT ||
         PreferenceManager.getDefaultSharedPreferences(context)
                          .getBoolean(ApplicationPreferencesActivity.ALL_SMS_PREF, true))
     {