Fix #578: check list mixed with empty content

[tomyeh]

Fix #578

Cause: taskListItemState not reset if the content is empty.

Alternatively, we can always call parseTaskListItem (instead of resetting taskListItemState)

[coveralls]

Pull Request Test Coverage Report for Build 7797221391

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 96.135%

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Totals
Change from base Build 7735606505:	0.0%
Covered Lines:	1542
Relevant Lines:	1604

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💛 - Coveralls