fix: Set Param::GuaranteeE2ee before preparing message blob (#8090)

Otherwise `Param::GuaranteeE2ee` is set only after rendering the message
and some UIs, e.g. DC Android, display the message as unencrypted while
preparing the blob and rendering and encrypting the message. NB: DC
Desktop doesn't display the message until `send_msg()` returns.

---------
Co-authored-by: Hocuri <hocuri@gmx.de>

src/message.rs

@@ -1392,6 +1392,8 @@ pub enum MessageState {
     /// For files which need time to be prepared before they can be
     /// sent, the message enters this state before
     /// OutPending.
+    ///
+    /// Deprecated 2024-12-07.
     OutPreparing = 18,
 
     /// Message saved as draft.