The other get! in DoubleDict (#1822)

* The other get in DoubleDict - followup from 1821

* fix space

Author: joaquimg

src/Utilities/DoubleDicts.jl

@@ -58,7 +58,10 @@ A type stable inner dictionary of [`DoubleDict`](@ref).
 mutable struct DoubleDictInner{F,S,V} <: AbstractDoubleDictInner{F,S,V}
     dict::Dict{Int64,V}
     function DoubleDictInner{F,S}(d::DoubleDict{V}) where {F,S,V}
-        return new{F,S,V}(get!(d.dict, (F, S), Dict{Int64,V}()))
+        if !haskey(d.dict, (F, S))
+            d.dict[(F, S)] = Dict{Int64,V}()
+        end
+        return new{F,S,V}(d.dict[(F, S)])
     end
 end