Graph weights are incorrect when points are near two intersecting edges

[mattwigway]

Consider a situation like this:

1-----2
| *
|
3

where the numbers are nodes and the * is a destination. We run create_graph_weights, which finds edges near the point, and proportionally assigns the weight to the nodes at the end of those edges. In this case, the nodes-at-end-of-edges array found will be [1, 2, 1, 3]. Note that node 1 is there twice, because it is at the end of both edges. We then update the weights with code that looks like this:

weights[nodes, i] .+= row[weightcol] / length(nodes)

The problem is that when there are duplicates in nodes, this will only update each of them once, e.g.

x = zeros(Float64, 3)
x[[2, 3, 2]] .+= 1 # => [0, 1, 1]

when the answer we want is [0, 2, 1] with one added to index 2 twice. This is easy enough to solve by just looping.

[mattwigway]

See also: https://discourse.julialang.org/t/unexpected-behavior-of-vectorized-with-duplicate-indices/112537