fix: update raw headers after changing messages to during parsing

Previously, headers were not updated but the mail gem parsing may decide
to change the transfer encoding. If it does this, the body is updated to
the new format but the header is not, this results in a mismatch when the
message it sent onwards and the client being unable render the message.

The specific situation identified was changing an HTML-only e-mail from
quoted-printable to 7bit.

closes #2816

lib/postal/message_db/message.rb

@@ -535,7 +535,9 @@ def parse_content
         if parse_result.actioned?
           #  Somethign was changed, update the raw message
           @database.update(raw_table, { data: parse_result.new_body }, where: { id: raw_body_id })
+          @database.update(raw_table, { data: parse_result.new_headers }, where: { id: raw_headers_id })
           @raw = parse_result.new_body
+          @raw_headers = parse_result.new_headers
           @raw_message = nil
         end
         update("parsed" => 1, "tracked_links" => parse_result.tracked_links, "tracked_images" => parse_result.tracked_images)

lib/postal/message_parser.rb

@@ -14,7 +14,7 @@ def initialize(message)
 
       return unless @domain
 
-      @parsed_output = generate
+      @parsed_output = generate.split("\r\n\r\n", 2)
     end
 
     attr_reader :tracked_links
@@ -25,7 +25,11 @@ def actioned?
     end
 
     def new_body
-      @parsed_output.split("\r\n\r\n", 2)[1]
+      @parsed_output[1]
+    end
+
+    def new_headers
+      @parsed_output[0]
     end
 
     private