Avoid the preprocess-function adding consecutive blank lines

[Snuffleupagus]

When pre-processor blocks are being removed, since they don't apply to the current build target, we may currently end up with consecutive blank lines.
While this is obviously not a big issue, it's nonetheless undesirable and we can adjust the writeLine function to prevent that.

[Snuffleupagus]

/botio integrationtest

[pdfjsbot]

From: Bot.io (Windows)

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Received

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

Live output at: http://54.193.163.58:8877/cff3f1999137808/output.txt

[pdfjsbot]

From: Bot.io (Linux m4)

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Received

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

Live output at: http://54.241.84.105:8877/948881f2b4d2131/output.txt

[pdfjsbot]

From: Bot.io (Linux m4)

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Success

Full output at http://54.241.84.105:8877/948881f2b4d2131/output.txt

Total script time: 4.29 mins

• Integration Tests: Passed

[pdfjsbot]

From: Bot.io (Windows)

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Success

Full output at http://54.193.163.58:8877/cff3f1999137808/output.txt

Total script time: 7.97 mins

• Integration Tests: Passed

[Snuffleupagus]

/botio-linux preview

[pdfjsbot]

From: Bot.io (Linux m4)

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Received

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

Live output at: http://54.241.84.105:8877/ea26299c6081ff6/output.txt

[pdfjsbot]

From: Bot.io (Linux m4)

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Success

Full output at http://54.241.84.105:8877/ea26299c6081ff6/output.txt

Total script time: 2.56 mins

Published

• Viewer: http://54.241.84.105:8877/ea26299c6081ff6/web/viewer.html
• Viewer (legacy): http://54.241.84.105:8877/ea26299c6081ff6/legacy/web/viewer.html

[calixteman]

LGTM.