fix: Email encoding issue - utf8 (#1264)

There were issues in parsing Arabic or UTF characters (emojis)
correctly for the incoming emails.

All these characters were converted to question marks which is
teh fallback character when an encoding is enforced and there is
a missing matching character.

app/presenters/mail_presenter.rb

@@ -12,7 +12,7 @@ class MailPresenter < SimpleDelegator
   end
 
   def text_content
-    @decoded_text_content ||= encode_to_unicode(text_part&.body&.decoded || fallback_content)
+    @decoded_text_content ||= encode_to_unicode(text_part&.decoded || fallback_content)
     @text_content ||= {
       full: @decoded_text_content,
       reply: extract_reply(@decoded_text_content)[:reply],
@@ -21,7 +21,7 @@ class MailPresenter < SimpleDelegator
   end
 
   def html_content
-    @decoded_html_content ||= encode_to_unicode(html_part&.body&.decoded || fallback_content)
+    @decoded_html_content ||= encode_to_unicode(html_part&.decoded || fallback_content)
     @html_content ||= {
       full: @decoded_html_content,
       reply: extract_reply(@decoded_html_content)[:reply],
@@ -70,6 +70,8 @@ class MailPresenter < SimpleDelegator
   # forcing the encoding of the content to UTF-8 so as to be compatible with database and serializers
   def encode_to_unicode(str)
     current_encoding = str.encoding.name
+    return str if current_encoding == 'UTF-8'
+
     str.encode(current_encoding, 'UTF-8', invalid: :replace, undef: :replace, replace: '?')
   end