stream_cdda, stream_vcd: check read buffer size

These assumed that the buffer provided with fill_buffer() was at least
sector sized, instead of checking the size parameter.

This is just a cleanup, since every caller made sure to align everything
on sector sizes, if a stream has the sector size set.

stream/stream_cdda.c

@@ -196,6 +196,9 @@ static int fill_buffer(stream_t *s, char *buffer, int max_len)
     int16_t *buf;
     int i;
 
+    if (max_len < CDIO_CD_FRAMESIZE_RAW)
+        return -1;
+
     if ((p->sector < p->start_sector) || (p->sector > p->end_sector)) {
         s->eof = 1;
         return 0;

stream/stream_vcd.c

@@ -79,6 +79,8 @@ static const struct m_struct_st stream_opts = {
 static int fill_buffer(stream_t *s, char* buffer, int max_len){
   if(s->pos > s->end_pos) /// don't past end of current track
     return 0;
+  if (max_len < VCD_SECTOR_DATA)
+    return -1;
   return vcd_read(s->priv,buffer);
 }