Heap leak in `h5str_convert()` for array and complex datatypes

[K-ANOY]

I found a possible heap leak in h5str_convert(). The H5T_ARRAY andH5T_COMPLEX cases allocate a temporary buffer with calloc(), but the buffer is never released.

File: java/src-jni/jni/h5util.c

Function: h5str_convert

Relevant code:

case H5T_ARRAY: {
    hsize_t i, dims[H5S_MAX_RANK], total_elmts;
    size_t  baseTypeSize;
    int     rank = 0;

    ...

    if (NULL == (cptr = (char *)calloc((size_t)total_elmts, baseTypeSize)))
        H5_OUT_OF_MEMORY_ERROR(ENVONLY, "h5str_convert: failed to allocate array buffer");

    for (i = 0; i < total_elmts; i++) {
        if (!(h5str_convert(ENVONLY, &this_str, container, mtid, out_buf, i * baseTypeSize))) {
            CHECK_JNI_EXCEPTION(ENVONLY, JNI_FALSE);
            goto done;
        }
        ...
    }

    ...
    break;
}

and:

case H5T_COMPLEX: {
    size_t baseTypeSize;

    ...

    if (NULL == (cptr = calloc(1, typeSize)))
        H5_OUT_OF_MEMORY_ERROR(ENVONLY, "h5str_convert: failed to allocate array buffer");

    /* Convert real part */
    if (!(h5str_convert(ENVONLY, &this_str, container, mtid, out_buf, 0))) {
        CHECK_JNI_EXCEPTION(ENVONLY, JNI_FALSE);
        goto done;
    }

    ...
    break;
}

The done block only closes mtid; it does not free the buffer allocated into
cptr:

done:
    if (mtid >= 0)
        H5Tclose(mtid);

    return retVal;

This happens on the ordinary success path for array and complex datatype
conversion, not only on an error path. The recursive calls write directly into
out_buf, so the allocated buffer also appears to be unused after allocation.

The function is reachable from JNI string write paths such as
H5AwriteVL_asstr() and H5DwriteVL_asstr(), which call h5str_convert() for
each string element before writing the converted buffer to HDF5.

Suggested fix: remove the unused calloc() allocations if they are not needed,
or keep them in a separate temporary pointer and release that pointer on every
exit path. Since cptr can also point into out_buf, the fix should avoid
blindly freeing cptr without tracking whether it owns heap memory.