Do not attempt to access empty data. Fixes #290.

Author: FrancescAlted

Diff for: src/blosc2/blosc2_ext.pyx

@@ -1010,7 +1010,7 @@ cdef class SChunk:
         cdef int64_t index
         cdef Py_buffer *buf
         cdef uint8_t *buf_ptr
-        if data is not None:
+        if data is not None and len(data) > 0:
             buf = <Py_buffer *> malloc(sizeof(Py_buffer))
             PyObject_GetBuffer(data, buf, PyBUF_SIMPLE)
             buf_ptr = <uint8_t *> buf.buf

Diff for: tests/test_tensor.py

@@ -128,6 +128,16 @@ def test_pack_tensor_array(size, dtype):
     assert np.array_equal(nparray, a2)
 
 
+def test_pack_tensor_empty():
+    empty = np.zeros((0,), dtype=float)
+    pempty = blosc2.pack_tensor(empty)
+
+    empty2 = blosc2.unpack_tensor(pempty)
+    assert np.array_equal(empty, empty2)
+    assert empty2.dtype == empty.dtype
+    assert empty2.shape == empty.shape
+
+
 ##### save / load  #####