Fix source span calculation for LineBreakInline

[zickb]

Fix the source span calculation of the last LineBreakInline in paragraph when multiple blocks exists.

I have added the source span calculation for the last LineBreakInline in #733, but the logic does not handle multiple blocks correctly. This corrects the logic.

[coveralls]

Pull Request Test Coverage Report for Build 7203562141

• 28 of 28 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.004%) to 93.146%

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Totals
Change from base Build 7185576836:	0.004%
Covered Lines:	26047
Relevant Lines:	27331

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💛 - Coveralls

[xoofx]

Thanks!