modules/services_discovery/sap.c: avoid out-of-bounds write

After OpenDemux reads data using stream_Read(), it writes a '\0' to
the buffer after the newly-read data, but if the stream returned exactly
i_read_max bytes, this '\0' will end up just past the end of the allocated
psz_sdp array (see the call to realloc at the beginning of the loop).
Adjust the realloc call to allocate this one extra byte.
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>
(cherry picked from commit dee928705dd32839317dca0e77089b02dd720763)

modules/services_discovery/sap.c

@@ -348,7 +348,7 @@ static int OpenDemux( vlc_object_t *p_this )
     for( i_len = 0, psz_sdp = NULL; i_len < 65536; )
     {
         const int i_read_max = 1024;
-        char *psz_sdp_new = realloc( psz_sdp, i_len + i_read_max );
+        char *psz_sdp_new = realloc( psz_sdp, i_len + i_read_max + 1 );
         size_t i_read;
         if( psz_sdp_new == NULL )
         {