Check if the Names dictionary actually contains a Dests dictionary before attempting to get the destinations

[Snuffleupagus]

Currently the unit test for getDestinations is partially disabled, see https://github.com/mozilla/pdf.js/blob/master/test/unit/api_spec.js#L68.

The problem with the file basicapi.pdf is that the Names dictionary is empty, so this PR makes sure that we check that before attempting to get the Dests.
This PR thus makes it possible to fix a, currently meaningless, unit test.

[Snuffleupagus]

/botio unittest

[pdfjsbot]

From: Bot.io (Linux)

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Received

Command cmd_unittest from @Snuffleupagus received. Current queue size: 0

Live output at: http://107.21.233.14:8877/31585c37b81bf56/output.txt

[pdfjsbot]

From: Bot.io (Windows)

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Received

Command cmd_unittest from @Snuffleupagus received. Current queue size: 0

Live output at: http://107.22.172.223:8877/35582bbd4df3d63/output.txt

[Snuffleupagus]

/botio-linux preview

[pdfjsbot]

From: Bot.io (Linux)

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Received

Command cmd_preview from @Snuffleupagus received. Current queue size: 1

Live output at: http://107.21.233.14:8877/bfcff31f26ee50d/output.txt

[pdfjsbot]

From: Bot.io (Linux)

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Success

Full output at http://107.21.233.14:8877/31585c37b81bf56/output.txt

Total script time: 0.61 mins

• Unit Tests: Passed

[pdfjsbot]

From: Bot.io (Windows)

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Success

Full output at http://107.22.172.223:8877/35582bbd4df3d63/output.txt

Total script time: 0.68 mins

• Unit Tests: Passed

[pdfjsbot]

From: Bot.io (Linux)

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Success

Full output at http://107.21.233.14:8877/bfcff31f26ee50d/output.txt

Total script time: 0.70 mins

Published

• Viewer: http://107.21.233.14:8877/bfcff31f26ee50d/web/viewer.html
• B2G Viewer: http://107.21.233.14:8877/bfcff31f26ee50d/extensions/b2g/content/web/viewer.html
• Extension: http://107.21.233.14:8877/bfcff31f26ee50d/extensions/firefox/pdf.js.xpi
• Extension (AMO): http://107.21.233.14:8877/bfcff31f26ee50d/extensions/firefox/pdf.js.amo.xpi

[yurydelendik]

Really good, thanks.