bindings: Add empty handle check in toV8(IDbAny*)
bindings: Add empty handle check in toV8(IDbAny*)

It would be better to return empty handle rather than half-baked object
when a toV8() call fails for an internal field.

BUG=479065

Review URL: https://codereview.chromium.org/1094283002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@194180 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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