Prevent insanely long passwords from crashing SystemUI

Bug: 22214934
Change-Id: I32e238e53ac4b6dd0ae6de226b98894c495b256f
diff --git a/packages/Keyguard/res/layout/keyguard_password_view.xml b/packages/Keyguard/res/layout/keyguard_password_view.xml
index b7d5d30..5433c4e3 100644
--- a/packages/Keyguard/res/layout/keyguard_password_view.xml
+++ b/packages/Keyguard/res/layout/keyguard_password_view.xml
@@ -58,6 +58,7 @@
              android:textSize="16sp"
              android:textAppearance="?android:attr/textAppearanceMedium"
              android:imeOptions="flagForceAscii|actionDone"
+             android:maxLength="500"
              />
 
          <ImageView android:id="@+id/switch_ime_button"