bug #137 [Debug] Fix #122 messagePart.charset not defined (SamMcSam)

This PR was merged into the 2.3-dev branch.

Discussion
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[Debug] Fix #122 messagePart.charset not defined

Fix for the error #122

``
 Method "charset" for object "Swift_Attachment" does not exist in @swiftmailer\Collector\swiftmailer.html.twig at line 170
``

that prevented the debug panel from opening when attaching files to mails.

It was already done once (#37) but came back with the new design.

Commits
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533927b [Debug] Fix #122 messagePart.charset not defined

Author: stof

Resources/views/Collector/swiftmailer.html.twig

@@ -167,7 +167,7 @@
                         <div class="card-block">
                             <span class="label">Alternative part ({{ messagePart.contentType }})</span>
                             <pre>
-                                {%- if messagePart.charset %}
+                                {%- if messagePart.charset is defined and messagePart.charset %}
                                     {{- messagePart.body|convert_encoding('UTF-8', messagePart.charset) }}
                                 {%- else %}
                                     {{- messagePart.body }}