Xon - Threadmarks Pro 2.18.6

• Fix pushing threadmark reactions to the thread's reaction totals would be reset when the first post was reacted to
• Fix "Add threadmark with backdate" permission not being respected when rendering the 'add threadmark' dialog. This permission was respected when actually adding the threadmark.

• Fix new threadmark alerts where being triggered for edits

• Fix merging threads would not merge threadmarks from source threads into the target thread in a predictable way.

• Harden threadmark index handling of threads which were unexpectedly hard-deleted

• Fix "Error rendering widget: ...setContentFromAlias(): Argument #1 must be of type string, null given"