fix(web): use a distinct salt for TOTP authentication

If TOTP is enabled for a user, it will be disabled until the user
configure it again, which will generate a new private salt.

SoObjects/SOGo/SOGoUser.m

@@ -1138,7 +1138,7 @@
 
   size_t s_len, secret_len;
 
-  key = [[[self userSettings] userSalt] substringToIndex: 12];
+  key = [[[self userSettings] userPrivateSalt] substringToIndex: 12];
   s = [key UTF8String];
   s_len = strlen(s);