Sometimes stray connection wires are left after object delete

[bgribble]

I'm not sure exactly when I see this, but it happens occasionally.

Also seen when accidentally selecting a wire without the endpoints and dragging a group.

[bgribble]

To reproduce:

• m "hello" RET c a p print RET RET to create a simple network
• RET foo RET to edit the print into an invalid processor
• DEL to delete the invalid processor

Note the connection from the message is still there.

[bgribble]

The commit above addresses the only instance of this problem I can really recall. Can reopen if it comes up again.