e4crypt_unlock_user_key no longer likes nullptr.

Bug: 27075797
Change-Id: I835d17d02ea50a88ef0a5322a30e04f3d0237019
diff --git a/Ext4Crypt.cpp b/Ext4Crypt.cpp
index b966b96..eaa08db 100644
--- a/Ext4Crypt.cpp
+++ b/Ext4Crypt.cpp
@@ -422,7 +422,7 @@
     // If this is a non-FBE device that recently left an emulated mode,
     // restore user data directories to known-good state.
     if (!e4crypt_is_native() && !e4crypt_is_emulated()) {
-        e4crypt_unlock_user_key(0, 0, nullptr, nullptr);
+        e4crypt_unlock_user_key(0, 0, "!", "!");
     }
 
     return 0;