This fixes an issue hit by GDAL, and that is found in netcdf 4.6.3
and 4.7.0
git bisect pointed the problem to have started with
```
77ab979c5f is the first bad commit
commit 77ab979c5f
Author: Ed Hartnett <edwardjameshartnett@gmail.com>
Date: Sat Jun 16 09:58:48 2018 -0600
using get_vars but not put_vars
:040000 040000 8611e77aaefc9ffd1d13 M libsrc4
```
where nc_get_vara_double() started using nc4_get_vars() underneath.
It turns out that nc4_get_vars() was buggy in the situation exercised by GDAL.
This can be reproduced with the following simple test case:
```
int main()
{
int status;
int cdfid = -1;
int first_dim;
int varid;
int other_var;
size_t anStart[NC_MAX_DIMS];
size_t anCount[NC_MAX_DIMS];
double* val = (double*)calloc(3, sizeof(double));
status = nc_create("foo.nc", NC_NETCDF4, &cdfid);
assert( status == NC_NOERR );
status = nc_def_dim(cdfid, "unlimited_dim", NC_UNLIMITED, &first_dim);
assert( status == NC_NOERR );
status = nc_def_var(cdfid, "my_var", NC_DOUBLE, 1, &first_dim, &varid);
assert( status == NC_NOERR );
status = nc_def_var(cdfid, "other_var", NC_DOUBLE, 1, &first_dim, &other_var);
assert( status == NC_NOERR );
status = nc_enddef(cdfid);
assert( status == NC_NOERR );
/* Write 3 elements to set the size of the unlimited dim to 3 */
anStart[0] = 0;
anCount[0] = 3;
status = nc_put_vara_double(cdfid, other_var, anStart, anCount, val);
assert( status == NC_NOERR );
/* Read 2 elements starting with index=1 */
anStart[0] = 1;
anCount[0] = 2;
status = nc_get_vara_double(cdfid, varid, anStart, anCount, val);
assert( status == NC_NOERR );
status = nc_close(cdfid);
assert( status == NC_NOERR );
free(val);
return 0;
}
```
Running it under Valgrind without this patch leads to
```
==19637==
==19637== Invalid write of size 8
==19637== at 0x4C326CB: memcpy@@GLIBC_2.14 (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==19637== by 0x4EDBE3D: NC4_get_vars (hdf5var.c:2131)
==19637== by 0x4EDA24C: NC4_get_vara (hdf5var.c:1342)
==19637== by 0x4E68878: NC_get_vara (dvarget.c:104)
==19637== by 0x4E69FDB: nc_get_vara_double (dvarget.c:815)
==19637== by 0x400C08: main (in /home/even/netcdf-c/build/test)
==19637== Address 0xb70e3e8 is 8 bytes before a block of size 24 alloc'd
==19637== at 0x4C2FB55: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==19637== by 0x4009E8: main (in /home/even/netcdf-c/build/test)
==19637==
```
77ffbce43b