recog.c apply_change_group ret zero if num_changes is 0.

[Joern Rennecke]

> * recog.c (apply_change_group): Return zero if no changes.

Don't do that.  That is not only in contradiction to the
function's description, it'll break a lot of optimizations
too, ones that test if a - possibly empty - set of required
changes works before installing another change.

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SuperH
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