Printf: don't zero pad Inf or NaN

[jmkuhn]

We currently have

julia> @sprintf("%07f", -Inf)
"-000Inf"

julia> @sprintf("%07f", NaN)
"0000NaN"

With this PR

julia> @sprintf("%07f", -Inf)
"   -Inf"

julia> @sprintf("%07f", NaN)
"    NaN"

which is the same as Julia 1.5.4 and agrees with the C standard.

[JeffBezanson]

Thank you; I wonder why that regressed in 1.6.

[jmkuhn]

Printf was completely rewritten #32859 for 1.6