output/httpd: initialize unflushed_input

This fixes the following valgrind warning occuring on the first call of
httpd_output_read_page:
==20124== Conditional jump or move depends on uninitialised value(s)
==20124==    at 0x425E65: httpd_output_read_page (httpd_output_plugin.c:240)
==20124==    by 0x426087: httpd_output_open (httpd_output_plugin.c:279)
==20124==    by 0x41D862: ao_open (output_plugin.h:206)
==20124==    by 0x41E133: audio_output_task (output_thread.c:590)

NEWS

@@ -2,6 +2,8 @@ ver 0.16.2 (2011/??/??)
 * decoder:
   - tremor: fix configure test
   - gme: detect end of song
+* output:
+  - httpd: fix uninitialized variable
 
 
 ver 0.16.1 (2011/01/09)

src/output/httpd_output_plugin.c

@@ -123,6 +123,7 @@ httpd_output_init(G_GNUC_UNUSED const struct audio_format *audio_format,
 
 	/* initialize metadata */
 	httpd->metadata = NULL;
+	httpd->unflushed_input = 0;
 
 	/* initialize encoder */