output/httpd: flush encoder after tag

Without the flush, ReadPage() may not return any data, or not all
data.  This may result in incomplete ddata the new "header" page,
corrupting streams with some encoders such as Vorbis.

Fixes #145

src/output/plugins/httpd/HttpdOutputPlugin.cxx

@@ -468,6 +468,7 @@ HttpdOutput::SendTag(const Tag &tag)
 
 		try {
 			encoder->SendTag(tag);
+			encoder->Flush();
 		} catch (const std::runtime_error &) {
 			/* ignore */
 		}