Wrong formatting for small numbers in SI mode

[iustin]

When formatting small (i.e. [1, 10)) in SI "all" mode, the numbers are formatted wrongly with 'deci' as base:

λ> formatValue (Left FormatSiAll) 1
(10,Just Deci)
λ> formatValue (Left FormatSiAll) 5
(50,Just Deci)

Both of these should be formatted without a unit (or, if issue #1 is implemented, with the base unit).

In binary mode or other SI modes, since only supraunitary units are used, things work OK.

[iustin]

/cc @copton