Pev fix error return#461

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pemmanuelviel wants to merge 2 commits intoflann-lib:masterfrom

pemmanuelviel:pev-fix-error-return

Commits on Jul 1, 2020

Clean: Make it clear we cast -1 to unsigned on purpose
pemmanuelviel
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Make the returned value for errors consistent with final choice in OpenCV version
pemmanuelviel
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