Disable registration lock reminders for <=KK devices

Fixes #7500

src/org/thoughtcrime/securesms/lock/RegistrationLockDialog.java

@@ -7,6 +7,7 @@ import android.content.Context;
 import android.content.DialogInterface;
 import android.graphics.Typeface;
 import android.os.AsyncTask;
+import android.os.Build;
 import android.support.annotation.NonNull;
 import android.support.v7.app.AlertDialog;
 import android.text.Editable;
@@ -43,7 +44,8 @@ public class RegistrationLockDialog {
   private static final String TAG = RegistrationLockDialog.class.getSimpleName();
 
   public static void showReminderIfNecessary(@NonNull Context context) {
-    if (!RegistrationLockReminders.needsReminder(context)) return;
+    if (!RegistrationLockReminders.needsReminder(context))    return;
+    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) return;
 
     AlertDialog dialog      = new AlertDialog.Builder(context, R.style.RationaleDialog)
                                              .setView(R.layout.registration_lock_reminder_view)

src/org/thoughtcrime/securesms/lock/RegistrationLockReminders.java

@@ -44,8 +44,13 @@ public class RegistrationLockReminders {
     long lastReminderInterval     = TextSecurePreferences.getRegistrationLockNextReminderInterval(context);
     long nextReminderInterval;
 
-    if (success) nextReminderInterval = INTERVAL_PROGRESSION.get(lastReminderInterval);
-    else         nextReminderInterval = INTERVAL_REGRESSION.get(lastReminderInterval);
+    if (success) {
+      if (INTERVAL_PROGRESSION.containsKey(lastReminderInterval)) nextReminderInterval = INTERVAL_PROGRESSION.get(lastReminderInterval);
+      else                                                        nextReminderInterval = INTERVAL_PROGRESSION.get(TimeUnit.HOURS.toMillis(6));
+    } else {
+      if (INTERVAL_REGRESSION.containsKey(lastReminderInterval))  nextReminderInterval = INTERVAL_REGRESSION.get(lastReminderInterval);
+      else                                                        nextReminderInterval = INTERVAL_REGRESSION.get(TimeUnit.HOURS.toMillis(12));
+    }
 
     TextSecurePreferences.setRegistrationLockLastReminderTime(context, System.currentTimeMillis());
     TextSecurePreferences.setRegistrationLockNextReminderInterval(context, nextReminderInterval);