matrix multiplication not supported?

julia> A = OffsetArray([1 2; 3 4], 0:1, 0:1)
2×2 OffsetArray(::Array{Int64,2}, 0:1, 0:1) with eltype Int64 with indices 0:1×0:1:
 1  2
 3  4

julia> b = OffsetArray([5; 6], 0:1)
2-element OffsetArray(::Array{Int64,1}, 0:1) with eltype Int64 with indices 0:1:
 5
 6

julia> A*b
ERROR: ArgumentError: offset arrays are not supported but got an array with index other than 1
Stacktrace:
 [1] require_one_based_indexing at .\abstractarray.jl:89 [inlined]
 [2] generic_matvecmul!(::OffsetArray{Int64,1,Array{Int64,1}}, ::Char, ::OffsetArray{Int64,2,Array{Int64,2}}, ::OffsetArray{Int64,1,Array{Int64,1}}) at C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.2\LinearAlgebra\src\matmul.jl:501
 [3] mul! at C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.2\LinearAlgebra\src\matmul.jl:77 [inlined]
 [4] *(::OffsetArray{Int64,2,Array{Int64,2}}, ::OffsetArray{Int64,1,Array{Int64,1}}) at C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.2\LinearAlgebra\src\matmul.jl:51
 [5] top-level scope at none:0

Reproduce the A*b example from the issue, then read LinearAlgebra/src/matmul.jl and the require_one_based_indexing path in abstractarray.jl shown in the stack trace. Determine the intended behavior for OffsetArray operands and add coverage for the demonstrated multiplication; done means the supported operation behaves correctly without the reported error.