Preserving band structure in concatenations

[andreasvarga]

Is any way to preserve the band structure in some concatenations, as for example, in the folowing construction:

A = BandedMatrix(0=>rand(10))
Ab = [A zeros(10,4); zeros(4,10) Diagonal(rand(4,4))]

with

Ab = 14×14 BandedMatrix{Float64} with bandwidths (0, 0):
 0.292548   ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅ 
  ⋅        0.230225   ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅
  ⋅         ⋅        0.800509   ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅
  ⋅         ⋅         ⋅        0.564469   ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅
  ⋅         ⋅         ⋅         ⋅        0.538882   ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅
  ⋅         ⋅         ⋅         ⋅         ⋅        0.838634   ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅
  ⋅         ⋅         ⋅         ⋅         ⋅         ⋅        0.575544   ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅
  ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅        0.322138   ⋅         ⋅         ⋅         ⋅         ⋅         ⋅
  ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅        0.610594   ⋅         ⋅         ⋅         ⋅         ⋅ 
  ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅        0.998941   ⋅         ⋅         ⋅         ⋅
  ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅        0.330766   ⋅         ⋅         ⋅
  ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅        0.604465   ⋅         ⋅
  ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅        0.754899   ⋅
  ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅         ⋅        0.10646

However the following produces an error

Ab = [A zeros(10,4); zeros(4,10) rand(4,4)]
ERROR: BandError: attempt to access BandedMatrix{Float64, Matrix{Float64}, Base.OneTo{Int64}} with bandwidths (0, 0) at band -1
Stacktrace:
 [1] checkbandmatch(A::BandedMatrix{Float64, Matrix{Float64}, Base.OneTo{Int64}}, V::Matrix{Float64}, kr::UnitRange{Int64}, jr::UnitRange{Int64})
   @ BandedMatrices C:\Users\Andreas\.julia\packages\BandedMatrices\KJZ2p\src\generic\Band.jl:175
 [2] setindex!(A::BandedMatrix{Float64, Matrix{Float64}, Base.OneTo{Int64}}, V::Matrix{Float64}, kr::UnitRange{Int64}, jr::UnitRange{Int64})
   @ BandedMatrices C:\Users\Andreas\.julia\packages\BandedMatrices\KJZ2p\src\banded\BandedMatrix.jl:760
 [3] typed_hvcat(::Type{Float64}, ::Tuple{Int64, Int64}, ::BandedMatrix{Float64, Matrix{Float64}, Base.OneTo{Int64}}, ::Vararg{AbstractVecOrMat})
   @ Base .\abstractarray.jl:2193
 [4] hvcat(::Tuple{Int64, Int64}, ::BandedMatrix{Float64, Matrix{Float64}, Base.OneTo{Int64}}, ::Vararg{AbstractArray{Float64}})
   @ Base .\abstractarray.jl:2160
 [5] top-level scope
   @ REPL[4]:1

It would be nice to automatically produce a banded matrix with suitable bandwith.