fix convert ambiguity

Author: Pietro Vertechi

src/structarray.jl

@@ -59,6 +59,7 @@ end
 StructArray(s::StructArray) = copy(s)
 
 Base.convert(::Type{StructArray}, v::AbstractArray) = StructArray(v)
+Base.convert(::Type{StructArray}, v::StructArray) = v
 
 function Base.similar(::Type{StructArray{T, N, C}}, sz::Dims) where {T, N, C}
     cols = map_params(typ -> similar(typ, sz), C)

test/runtests.jl

@@ -110,6 +110,7 @@ end
     @test t2 == t
     t3 = StructArray(t)::StructArray
     @test t3 == t
+    @test convert(StructArray, t) == t
 end
 
 @testset "tuple case" begin