forward html-messages properly (#2151)

* add failing tests for forwarding html-mails

* let MsgId.get_html() return an option

* write html-part to local database on forwarding

* add html-part to forwarded non-dc messages

* read HTML-parts from encrypted messages

* avoid clone()

* Received:-header is no longer needed since #2152

* Update src/html.rs

Co-authored-by: Floris Bruynooghe <flub@devork.be>

* Update src/html.rs

Co-authored-by: Floris Bruynooghe <flub@devork.be>

* Update src/mimeparser.rs

Co-authored-by: Floris Bruynooghe <flub@devork.be>

* prefer 'orig' over 'org' as abbreviation for 'original'

* improve comment on tests

* prefer 'try_into()' over 'as u32' to avoid panics on bad data

* simplify ffi

Co-authored-by: Floris Bruynooghe <flub@devork.be>

src/mimeparser.rs

@@ -69,6 +69,12 @@ pub struct MimeMessage {
     // if this flag is set, the parts/text/etc. are just close to the original mime-message;
     // clients should offer a way to view the original message in this case
     pub is_mime_modified: bool,
+
+    /// The decrypted, raw mime structure.
+    ///
+    /// This is non-empty only if the message was actually encrypted.  It is used
+    /// for e.g. late-parsing HTML.
+    pub decoded_data: Vec<u8>,
 }
 
 #[derive(Debug, PartialEq)]
@@ -136,7 +142,7 @@ impl MimeMessage {
         headers.remove("chat-verified");
 
         // Memory location for a possible decrypted message.
-        let mail_raw;
+        let mut mail_raw = Vec::new();
         let mut gossipped_addr = Default::default();
 
         let (mail, signatures, warn_empty_signature) =
@@ -228,6 +234,7 @@ impl MimeMessage {
             group_avatar: None,
             failure_report: None,
             is_mime_modified: false,
+            decoded_data: Vec::new(),
         };
         parser.parse_mime_recursive(context, &mail).await?;
         parser.maybe_remove_bad_parts();
@@ -240,6 +247,10 @@ impl MimeMessage {
             }
         }
 
+        if parser.is_mime_modified {
+            parser.decoded_data = mail_raw;
+        }
+
         Ok(parser)
     }