When header spans multiple lines, it is incorrectly transcribed from msg to eml

[lolo101]

It is possible to check in MBoxWriterViaJavaMailTest

for instance, this test fails because the second recipient is missing:

    @Test
    void test_rcpt() throws Exception {
        ModuleLauncher.BaseConfigureLogging();

        try (FileSystem fileSystem = Jimfs.newFileSystem()) {
            Path testOut = fileSystem.getPath("test_out.eml");
            try (OutputStream outputStream = Files.newOutputStream(testOut)) {
                Message msg = givenMessage("/danke.msg");
                MBoxWriterViaJavaMail writer = givenWriter();
                writer.write(msg, outputStream);
            }
            assertThat(Files.readString(testOut)).contains("To: 'Andrea Pirchl' <a.pirchl@gmx.at>; 'Martin Oberzalek' <kingleo@gmx.at>");
        }
    }