exmdb: check return value of set_content_type calls

CID 1559995: (#1 of 1): Unchecked return value (CHECKED_RETURN)
CID 1559999: (#1 of 1): Unchecked return value (CHECKED_RETURN)
CID 1560002: (#1 of 1): Unchecked return value (CHECKED_RETURN)
14. check_return: Calling set_content_type without checking return
value (as is done elsewhere 23 out of 27 times).

Author: jengelh

exch/exmdb/message.cpp

@@ -2726,7 +2726,8 @@ static ec_error_t message_forward_message(const rulexec_in &rp,
 		auto pmime = imail1.add_head();
 		if (pmime == nullptr)
 			return ecServerOOM;
-		pmime->set_content_type("message/rfc822");
+		if (!pmime->set_content_type("message/rfc822"))
+			mlog(LV_WARN, "W-1767: set_content_type not successful, investigate");
 		/*
 		 * OXORULE v21 §2.2.5.1.1 specifies FWD_AS_ATTACHMENT is
 		 * exclusive, so FWD_PRESERVE_SENDER is not evaluated to build

lib/mapi/oxcmail.cpp

@@ -4000,7 +4000,8 @@ static bool smime_signed_writeout(MAIL &origmail, MIME &origmime,
 		auto s = fmt::format("[Message is not a valid OXOSMIME message. "
 			 "The attachment object is not of type multipart/signed.]");
 		origmime.write_content(s.c_str(), s.size(), mime_encoding::none);
-		origmime.set_content_type("text/plain");
+		if (!origmime.set_content_type("text/plain"))
+			/* ignore */;
 		return TRUE;
 	}
 	if (buf[16] != '\0' && buf[16] != ';')

mda/exmdb_local/auto_response.cpp

@@ -187,7 +187,8 @@ void auto_response_reply(const char *user_home,
 		put_context(pcontext);
 		return;
 	}
-	pmime->set_content_type(content_type);
+	if (!pmime->set_content_type(content_type))
+		mlog(LV_WARN, "W-1777: set_content_type unsuccessful");
 	if (*charset != '\0')
 		pmime->set_content_param("charset", charset);
 	pmime->set_field("From", from);