Defensively load untrusted icons from account authenticator

Catch Resources.NotFoundException which should cover all parsing
errors from loadDrawables(); also substitute a default icon if
parsing returns null.

Bug: 17760671
Change-Id: Ia0ec25e34974ed85b6ffe6882d5bce003d64e9d6

src/com/android/settings/accounts/AuthenticatorHelper.java

@@ -96,7 +96,8 @@ final public class AuthenticatorHelper extends BroadcastReceiver {
     /**
      * Gets an icon associated with a particular account type. If none found, return null.
      * @param accountType the type of account
-     * @return a drawable for the icon or null if one cannot be found.
+     * @return a drawable for the icon or a default icon returned by
+     * {@link PackageManager#getDefaultActivityIcon} if one cannot be found.
      */
     public Drawable getDrawableForType(Context context, final String accountType) {
         Drawable icon = null;