Crash in b2UpdateBodyMassData because of missing increment of loop variable

[simonvanbernem]

Hi,

while trying to update to the latest box2d commit, my game started crashing here, because the inertia was NaN: https://github.com/erincatto/box2d/blob/3a4f0da8374af61293a03021c9a0b3ebcfe67948/src/body.c#L626

This happens because this code doesn't increment shapeIndex before continuing, which causes the same shape mass data to be overwritten with 0 over and over, leaving garbage data in the remaining ones.

https://github.com/erincatto/box2d/blob/3a4f0da8374af61293a03021c9a0b3ebcfe67948/src/body.c#L589-L590

Adding shapeIndex += 1; fixes the crash

[erincatto]

Easy solve, stop using 0 density. :)

[erincatto]

Thanks for the report. Fixed in #1022