fix strange garbage results

needs to be reviewed by maintainers

libsrc/memio.c

@@ -382,8 +382,9 @@ fprintf(stderr,"memio_open: initial memory: %lu/%lu\n",(unsigned long)memio->mem
  (void)close(fd);
  }
 
- /* Use half the filesize as the blocksize ; why? */
- sizehint = filesize/2;
+ /* Return 8192 as large values cause: https://github.com/Unidata/netcdf-c/issues/401 Why? 
+ Note: File modes use: blksize(fd); */
+ sizehint = 8192;
 
  fd = nc__pseudofd();
  *((int* )&nciop->fd) = fd;