data_rowrange bug

[max-vassili3v]

I found a bug with indexing rows of a BandedMatrix whose data matrix is one row:

julia> a = BandedMatrix(ones(2,5), (0,0))
2×5 BandedMatrix{Float64} with bandwidths (0, 0):
 1.0   ⋅    ⋅    ⋅    ⋅
  ⋅   1.0   ⋅    ⋅    ⋅

julia> a[1,:]
ERROR: ArgumentError: step cannot be zero
Stacktrace:
 [1] steprange_last
   @ .\range.jl:338 [inlined]
 [2] StepRange
   @ .\range.jl:325 [inlined]
 [3] range_start_step_length(a::Int64, step::Int64, len::Int64)
   @ Base .\range.jl:216
 [4] _range
   @ .\range.jl:168 [inlined]
 [5] range
   @ .\range.jl:147 [inlined]
 [6] data_rowrange
   @ d:\Documents\Github\BandedMatrices.jl\src\banded\BandedMatrix.jl:575 [inlined]
 [7] getindex(A::BandedMatrix{Float64, Matrix{Float64}, Base.OneTo{Int64}}, k::Int64, ::Colon)
   @ BandedMatrices d:\Documents\Github\BandedMatrices.jl\src\banded\BandedMatrix.jl:443
 [8] top-level scope
   @ REPL[23]:1

I added a fix and unit tests to go with it.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.84%. Comparing base (47c15ab) to head (80947a5).
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #453      +/-   ##
==========================================
+ Coverage   89.61%   89.84%   +0.23%     
==========================================
  Files          25       25              
  Lines        3571     3643      +72     
==========================================
+ Hits         3200     3273      +73     
+ Misses        371      370       -1     

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[dlfivefifty]

A simpler fix might be to use StepRangeLen that allows zero steps:

julia> StepRangeLen(2,0,3)
StepRangeLen(2, 0, 3)

julia> collect(StepRangeLen(2,0,3))
3-element Vector{Int64}:
 2
 2
 2
```