[Toybox] find and {}

[enh]

from the top of find.c:

 * Not treating two {} as an error, but only using last

this came up today, specifically that this didn't work the same way
that GNU find would:

$ adb shell 'find /data/local/tmp -type d -exec echo {} {}.suffix \;'
/data/local/tmp {}.suffix

but i'm not sure whether that comment in the source is meant to be a
TODO or an expected deviation for a reason? (so i thought i'd ask
before i tried to fix it...)