[FIX] Theme build

[sebbi08]

Themes should also build if there is an librariesPattern provided but no library found

Fixes: #110

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[coveralls]

Pull Request Test Coverage Report for Build 493

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.5%) to 53.741%

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Totals
Change from base Build 491:	0.5%
Covered Lines:	1489
Relevant Lines:	2506

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💛 - Coveralls

[RandomByte]

Thanks @sebbi08!

LGTM. @matz3 what do you think?

[RandomByte]

@matz3 also agrees with this change 😃

We'll release this today. Thanks again!