Triple pipes used in tables incorrectly start a Sequence Diagram

[iCollin]

Reproduction Steps:

Create a table with some empty columns, followed by a sequence diagram:

|id|name|phone|email|address|
|:---|:---|:--------|:---------|:----------|
|0|bob|911|bob@gmail.com||
|1|alice|248|||

|||
User Registration Diagram
![UserRegistration](../assets/img/user_registration.diagram)
|||

Expected Behavior:
The user registration diagram is created as a sequence diagram after the user table.

Observed Behavior:
The ||| in the table that is indicating empty columns is treated as the start of a sequence diagram.

Potential Fixes:
Start a sequence diagram exclusively when the triple pipe is the ONLY content of a line. (no preceding or following characters)

[alflanagan]

This issue should have been filed against DocDown-Python instead. Leaving this open to add a test for the specific problem (which passes).