Fix crash when PTT is too short

The PTT that is allocated and read is smaller than what gets referenced.
The data is byte-swapped in place which results in writes to memory
locations outside the allocated region. Region 1 True Grit is an
example of this.

src/ifo_read.c

@@ -1184,6 +1184,10 @@ int ifoRead_VTS_PTT_SRPT(ifo_handle_t *ifofile) {
     goto fail;
   }
 
+  if(vts_ptt_srpt->nr_of_srpts > info_length / sizeof(*data)) {
+    fprintf(stderr, "libdvdread: PTT search table too small.\n");
+    goto fail;
+  }
   for(i = 0; i < vts_ptt_srpt->nr_of_srpts; i++) {
     B2N_32(data[i]);
     /* assert(data[i] + sizeof(ptt_info_t) <= vts_ptt_srpt->last_byte + 1);