hough_circle_gradient: centers could hold 0 in CartesianIndex

centers calculation could result in 0 in CartesianIndex. which is invalid value for array referencing in Julia

julia> centers, radii = hough_circle_gradient(img_edges, img_phase, 20:30, vote_threshold=2);

julia> img_demo = Float64.(img_edges); for c in centers img_demo[c] = 2; end
ERROR: BoundsError: attempt to access 312×252 Array{Float64,2} at index [152, 0]
Stacktrace:
 [1] setindex! at ./array.jl:769 [inlined]
 [2] setindex!(::Array{Float64,2}, ::Int64, ::CartesianIndex{2}) at ./multidimensional.jl:460
 [3] top-level scope at ./REPL[40]:1 [inlined]
 [4] top-level scope at ./none:0

julia> centers
96-element Array{CartesianIndex{2},1}:
 CartesianIndex(152, 0)  
 ⋮                       
 CartesianIndex(0, 40)   

Probably this happens during executing this statement: center=(center-1*one(center))*scale

julia> c = CartesianIndex(1, 2)
CartesianIndex(1, 2)

julia> c = (c - 1*one(c))
CartesianIndex(0, 1)

Start at the hough_circle_gradient entry point and inspect the centers calculation, especially center=(center-1*one(center))*scale. Reproduce the issue with the supplied Julia example and verify that the returned centers can be used for array indexing without producing zero coordinates.