demux: Initialize local variable.

gcc 4.6 reports:
  demux.c: In function HandleSection:
  demux.c:2267:61: warning: f may be used uninitialized in this function [-Wuninitialized]
  demux.c:2261:26: note: f was declared here

The gcc is correct that f is used initialized which is real bug in
this case.
Signed-off-by: Georgi Chorbadzhiyski <gf@unixsol.org>

demux.c

@@ -2258,7 +2258,7 @@ static void HandlePMT( uint16_t i_pid, uint8_t *p_pmt, mtime_t i_dts )
             if ( b_enable_ecm )
             {
                 k = 0;
-                uint16_t f;
+                uint16_t f = 0;
                 uint8_t *p_pmt_es;
                 while ((p_desc = descs_get_desc( pmtn_get_descs( p_es ), k++ )) != NULL)
                 {