[bugfix] Make sure loop connected pins are not hidden

[kvid]

• Resolves #263 that describes warnings and weird loop drawing because loop connected pins are hidden when hide_disconnected_pins=True.
• Activate loop pins as early as possible to enable correct counting of connected pins when connector.additional_components.qty_multiplier=populated.
• Check that loop pins actually exist before activating them.

I suggest a squash merge with the bullets above in the commit message body, and this commit message title:

Make sure loop connected pins are not hidden (#264)