Moved misplaced allDataReceived() assert

The spots where allDataReceived() was checked in an if statement, or
asserted against were switched, so the release build was going right
through the code in getYUVComponentSizes(), without returning early,
which could lead to a crash.

Added safety checks inside the JPEG decoder just in case we get into
this situation some other way.

BUG=410788,410586

Review URL: https://codereview.chromium.org/528293003

git-svn-id: svn://svn.chromium.org/blink/trunk@181439 bbb929c8-8fbe-4397-9dbb-9b2b20218538