Cells slider maybe has rounding errors

[phet-steele]

Each increment of the Cells slider, on the third screen, does not necessarily increase/decrease the number of cells displayed (depending on the direction you slide, of course).

Once you hit three, the fun begins. Each positive increment (dragging very slowly) will follow the order of: subtract one, add two, add one, subtract one, add two, add one, ....etc.

Seen on macOS 10.12.3 Chrome. For phetsims/tasks/issues/776.

URL: http://www.colorado.edu/physics/phet/dev/html/gene-expression-essentials/1.0.0-dev.2/gene-expression-essentials_en.html
Version: 1.0.0-dev.2 2017-01-30 19:21:44 UTC
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[phet-steele]

The fix looks good, thanks @aadish. Now each increment of the slider, while not guaranteed to create a new cell, will at least not decrement the number of visible cells. This is fine, most people probably won't slide one tick at a time anyway 😄.