Avoid giving GMime a NULL MIME-stream filter.

Micah Anderson reported an issue where a message failed to display in
the emacs interface, (it instead gave an error, "json-read-string: Bad
string format").

Micah tracked this down to the json output from "notmuch show" being
interrupted by a GMime error message:

	gmime-CRITICAL **: g_mime_stream_filter_add: assertion
	`GMIME_IS_FILTER (filter)

I tracked this down further to notmuch passing a NULL value to
g_mime_stream_filter_add. And this was due to calling
g_mime_filter_charset_new with a value of "unknown-8bit".

So we add a test message withe a Conten-Type of "text/plain;
charset=unknown-8bit" from Micah's message. Then we fix "notmuch show"
to test for NULL before calling g_mime_stream_filter_add. Bug fixed.

1 files changed, 9 insertions, 3 deletions

diff --git a/notmuch-show.c b/notmuch-show.c
index 26449fa5..4ed5fc74 100644
--- a/notmuch-show.c
+++ b/notmuch-show.c
@@ -225,9 +225,15 @@ show_part_content (GMimeObject *part, GMimeStream *stream_out)
 	g_mime_stream_filter_add(GMIME_STREAM_FILTER(stream_filter),
 				 g_mime_filter_crlf_new(FALSE, FALSE));
         if (charset) {
-          g_mime_stream_filter_add(GMIME_STREAM_FILTER(stream_filter),
-                                   g_mime_filter_charset_new(charset, "UTF-8"));
-        }
+	    GMimeFilter *charset_filter;
+	    charset_filter = g_mime_filter_charset_new(charset, "UTF-8");
+	    /* This result can be NULL for things like "unknown-8bit".
+	     * Don't set a NULL filter as that makes GMime print
+	     * annoying assertion-failure messages on stderr. */
+	    if (charset_filter)
+		g_mime_stream_filter_add(GMIME_STREAM_FILTER(stream_filter),
+					 charset_filter);
+	}
     }
 
     wrapper = g_mime_part_get_content_object (GMIME_PART (part));