[Bug] getStrokes returns NaN when provided two or more points with the same coordinates

[Julius Tarng]

getStroke([
  [1, 1],
  [1, 1],
])

ends up with

this can happen when sampling points on each frame (as opposed to onmousemove)

im not sure what the best expected result is, maybe drawing the points as a single dot/circle? or return an empty array if any of the results are NaN

[Steve Ruiz]

Good catch! Fixed in 629d767