Printf %g behaves strangely with 0 precision.

Discovered during #14331.

Namely these cases.

```
julia> @sprintf("%#.0g", 42)
"4.200000e+01"
c-> "4.e+01"

julia> @sprintf("%.0g", 42)
"4.2e+01"
c-> "4e+01"

julia> @sprintf("%.0g", 42.3)
"4.23e+01"
c-> "4e+01"
```

I'll be happy to take it.
