Incorrect single private message thread description

[johnjamesjacoby]

When a member private messages themselves, they see a description that says:

"Conversation between and you."

single.php attempts to check ! bp_get_thread_recipients_count() but this doesn't account for 1 single person messaging themselves.

[boonebgorges]

For the record: the logic in BP_Messages_Thread::get_recipients() ensures that the thread recipient count will correctly be 1 in cases like this, which means we can safely rely on it for a <= check.

Looks good to me.

[johnjamesjacoby]

In 9296:

When a member sends themselves a private message (helpful for testing, mostly) ensure they see the appropriate description. Fixes #6087.

[johnjamesjacoby]

In 9407:

Update single message conversation verbiage in single.php. Fixes #6087 again, but better this time.