Support vcat of vcat

[dlfivefifty]

This should work in both cases:

julia> vcat(2, vcat(1, Zeros(∞)))
∞-element LazyArrays.CachedArray{Float64,1,Array{Float64,1},Zeros{Float64,1,Tuple{InfiniteArrays.OneToInf{Int64}}}} with indices OneToInf():
 2.0
 1.0
 0.0
 0.0
 0.0
 0.0
 0.0
 0.0
 ⋮
julia> vcat(2, vcat(1, Fill(2,∞)))
^CERROR: InterruptException:
Stacktrace:
 [1] Array at ./boot.jl:406 [inlined]
 [2] similar at ./array.jl:379 [inlined]
 [3] _vec_resizedata!(::LazyArrays.CachedArray{Int64,1,Array{Int64,1},Zeros{Int64,1,Tuple{InfiniteArrays.OneToInf{Int64}}}}, ::Int64) at /Users/sheehanolver/Projects/LazyArrays.jl/src/cache.jl:128
 [4] resizedata! at /Users/sheehanolver/Projects/LazyArrays.jl/src/cache.jl:139 [inlined]
 [5] resizedata! at /Users/sheehanolver/Projects/LazyArrays.jl/src/cache.jl:114 [inlined]
 [6] setindex! at /Users/sheehanolver/Projects/LazyArrays.jl/src/cache.jl:72 [inlined]
 [7] setindex! at ./subarray.jl:298 [inlined]
 [8] copyto_unaliased!(::IndexCartesian, ::SubArray{Int64,1,LazyArrays.CachedArray{Int64,1,Array{Int64,1},Zeros{Int64,1,Tuple{InfiniteArrays.OneToInf{Int64}}}},Tuple{InfiniteArrays.InfUnitRange{Int64}},false}, ::IndexCartesian, ::Fill{Int64,1,Tuple{InfiniteArrays.OneToInf{Int64}}}) at ./abstractarray.jl:874
 [9] copyto!(::SubArray{Int64,1,LazyArrays.CachedArray{Int64,1,Array{Int64,1},Zeros{Int64,1,Tuple{InfiniteArrays.OneToInf{Int64}}}},Tuple{InfiniteArrays.InfUnitRange{Int64}},false}, ::Fill{Int64,1,Tuple{InfiniteArrays.OneToInf{Int64}}}) at ./abstractarray.jl:840
 [10] _copyto!(::LazyArrays.PaddedLayout{DenseColumnMajor}, ::FillLayout, ::SubArray{Int64,1,LazyArrays.CachedArray{Int64,1,Array{Int64,1},Zeros{Int64,1,Tuple{InfiniteArrays.OneToInf{Int64}}}},Tuple{InfiniteArrays.InfUnitRange{Int64}},false^Cnt64ERROR: InterruptException:
Stacktrace:
 [1] sigatomic_end at ./c.jl:425 [inlined]
 [2] uv_write(::Base.TTY, ::Ptr{UInt8}, ::UInt64) at ./stream.jl:929
 [3] unsafe_write(::Base.TTY, ::Ptr{UInt8}, ::UInt64) at ./stream.jl:1005
 [4] unsafe_write at ./io.jl:337 [inlined]
 [5] unsafe_write at ./io.jl:622 [inlined]
 [6] write at ./io.jl:686 [inlined]
 [7] print at ./show.jl:210 [inlined]
 [8] show_sym(::IOContext{Base.TTY}, ::Symbol; allow_macroname::Bool) at ./show.jl:1086
 [9] show_sym at ./show.jl:1085 [inlined]
 [10] show_type_name(::IOContext{Base.TTY}, ::Core.TypeName) at ./show.jl:591
 [11] show_datatype(::IOContext{Base.TTY}, ::DataType) at ./show.jl:618
 [12] show(::IOContext{Base.TTY}, ::Type) at ./show.jl:497
 [13] show_datatype(::IOContext{Base.TTY}, ::DataType) at ./show.jl:612
 [14] show(::IOContext{Base.TTY}, ::Type) at ./show.jl:497
 [15] show_datatype(::IOContext{Base.TTY}, ::DataType) at ./show.jl:612
 [16] show(::IOContext{Base.TTY}, ::Type) at ./show.jl:497
 [17] show_datatype(::IOContext{Base.TTY}, ::DataType) at ./show.jl:612
 [18] show(::IOContext{Base.TTY}, ::Type) at ./show.jl:497
 [19] print(::IOContext{Base.TTY}, ::Type{T} where T) at ./strings/io.jl:35
 [20] print(::IOContext{Base.TTY}, ::String, ::Type{T} where T) at ./strings/io.jl:46
 [21] show_tuple_as_call(::IOContext{Base.TTY}, ::Symbol, ::Type{T} where T, ::Bool, ::Nothing) at ./show.jl:1788
 [22] show_tuple_as_call(::IOContext{Base.TTY}, ::Symbol, ::Type{T} where T, ::Bool) at ./show.jl:1755
 [23] show_spec_linfo(::IOContext{Base.TTY}, ::Base.StackTraces.StackFrame) at ./stacktraces.jl:242
 [24] show(::IOContext{Base.TTY}, ::Base.StackTraces.StackFrame; full_path::Bool) at ./stacktraces.jl:253
 [25] show_trace_entry(::IOContext{Base.TTY}, ::Base.StackTraces.StackFrame, ::Int64; prefix::String) at ./errorshow.jl:555
 [26] show_backtrace(::IOContext{Base.TTY}, ::Array{Base.StackTraces.StackFrame,1}) at ./errorshow.jl:659
 [27] showerror(::IOContext{Base.TTY}, ::InterruptException, ::Array{Base.StackTraces.StackFrame,1}; backtrace::Bool) at ./errorshow.jl:93
 [28] showerror at ./errorshow.jl:88 [inlined]
 [29] display_repl_error(::Base.TTY, ::InterruptException, ::Array{Base.StackTraces.StackFrame,1}) at /Users/sheehanolver/.vscode/extensions/julialang.language-julia-1.0.4/scripts/packages/VSCodeServer/src/repl.jl:104
 [30] display_repl_error(::Base.TTY, ::LoadError, ::Array{Base.StackTraces.StackFrame,1}) at /Users/sheehanolver/.vscode/extensions/julialang.language-julia-1.0.4/scripts/packages/VSCodeServer/src/repl.jl:107
 [31] evalrepl(::Module, ::String, ::REPL.LineEditREPL, ::REPL.LineEdit.Prompt) at /Users/sheehanolver/.vscode/extensions/julialang.language-julia-1.0.4/scripts/packages/VSCodeServer/src/repl.jl:84
 [32] top-level scope at /Users/sheehanolver/.vscode/extensions/julialang.language-julia-1.0.4/scripts/packages/VSCodeServer/src/repl.jl:73