BlobOp.read

glong read(gda.blob.Blob blob, glong offset, glong size)

Reads a chunk of bytes from the BLOB accessible through op into blob.

`blob`	a #GdaBlob to read data to
`offset`	offset to read from the start of the blob (starts at 0)
`size`	maximum number of bytes to read.

the number of bytes actually read. In case of error, -1 is returned and the

provider should have added an error to the connection.