When returning the column or row index of a given cell, guard against the column count being 0 or the given index being out of bounds of the current grid or table. The MSAA code already did this previously, but now the upper bounds check has been moved to the base classes and an additional guard for the column count been put in place so a division by 0 crash canot happen.
A return value for RowIndexAt and ColIndexAt of -1 indicates an error condition. ATK will automatically deal with this, and the IA2 code has been adjusted to check for this and return an invalid argument error in such cases, too.
Differential Revision: https://phabricator.services.mozilla.com/D18931
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extra : moz-landing-system : lando
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