display a warning when a frame has negative values

[kevinvangelder]

details_row: One or more values in your frame is a negative or zero. If this is unexpected, check your styles.
Frame values: {l: 10, t: 796.0, w: 355.0, h: -129.0}

[squidpunch]

:+1:

[carlinisaacson]

Very nice! :+1: I was actually going to suggest checking for zero as well when you suggested this feature.