[FIX]Empty binary column download error

1.Empty file must not show as a hyperlink
2.When active hyperlink to invoke "/web/binary/saveas"
That change seems odd.

As far as I can read it, it tries to see if `value` is bin_size formatted. bin_size yields a number (integer or float), a space and a unit (MB, KB, …). If there is *no* space in the value (== -1) it assumes the value is valid base64 data and creates the download link inline (since it already has all necessary data), otherwise it creates an indirection through `/web/binary/saveas`