GridLocations nondeterministically returns incorrect result inside Builder

[MatthiasJ1]

@jdegenstein reports the following snippet nondeterministically fails

with BuildSketch() as s:
    with GridLocations(2,2,25,25):
        Rectangle(1,1)
assert len(s.sketch.faces()) == 25*25

other variations work so this appears to be an issue limited to the Builder API

s = Sketch() + GridLocations(2,2,25,25) * Rectangle(1,1)
assert len(s.faces()) == 25*25 # ok

[gumyr]

With the above fix this failure doesn't happen after at least 100 attempts.