fix: image/*, audio/*, video/* are not attachments when found in both…

… text and html parts

RFC8621 section 4.1.4
The additional is_multipart heuristic is to prevent the current malformed .eml
tests from failing.

src/parsers/message.rs

@@ -323,20 +323,19 @@ impl MessageParser {
                         }
                         (Cow::Borrowed(bytes), None) => String::from_utf8_lossy(bytes),
                     };
-
                     let is_html = mime_type == MimeType::TextHtml;
 
-                    if add_to_html && !is_html {
+                    if add_to_html {
                         message.html_body.push(message.parts.len());
-                    } else if add_to_text && is_html {
+                    }
+                    if add_to_text {
                         message.text_body.push(message.parts.len());
                     }
 
-                    if add_to_html && is_html {
-                        message.html_body.push(message.parts.len());
-                    } else if add_to_text && !is_html {
-                        message.text_body.push(message.parts.len());
-                    } else {
+                    if !is_multipart && !(add_to_text || add_to_html)
+                        || (mime_type == MimeType::Inline || is_multipart)
+                            && (!add_to_text || !add_to_html)
+                    {
                         message.attachments.push(message.parts.len());
                     }
 
@@ -352,8 +351,12 @@ impl MessageParser {
                     if add_to_text {
                         message.text_body.push(message.parts.len());
                     }
-
-                    message.attachments.push(message.parts.len());
+                    if !is_multipart && !(add_to_text || add_to_html)
+                        || (mime_type == MimeType::Inline || is_multipart)
+                            && (!add_to_text || !add_to_html)
+                    {
+                        message.attachments.push(message.parts.len());
+                    }
 
                     if !is_inline {
                         PartType::Binary(bytes)