DPS preview when swapping out lynchpin gem shows output for next default skill, sometimes misleadingly

• What happened?

Messing with supports for a minion, I had their Infernal Legion DPS selected for Main Skill. When I then moved to the dropdown for picking a different support in the Infernal Legion slot, the preview tooltip claimed that changing to Elemental Focus would give me an unrealistic +1M DPS boost.

If I select the gem previewed, it changes my Main Skill to Minion Instability, with the resulting DPS matching the "+DPS inc. Poison" part of the strange preview. I'm not sure where the +1M Total DPS comes from.

• What were you trying to do?

No clear use case here--you typically don't want to be swapping out the gem that gives you your "Main Skill" DPS anyway. It was an accidental encounter while exploring gem options. But in a less obviously-wrong case it could mislead someone about their DPS prospects!

• What steps will reproduce the bug?

1. Create a new build
2. Add a minion skill and Infernal Legion support
3. Go to the dropdown from Infernal Legion and hover over a different support. Note the possibly strange preview numbers
4. Select the new gem. The Main Skill changes, with its numbers resembling the preview.

• Does it reproduce every time? If not, why so?

Yes, although the specific numbers vary wildly depending on the rest of the build's setup.

• Additional information:

https://pastebin.com/EnA8AuZk

Suggested fix would be to have any such preview say that it's removing all the DPS, making clear that you're effectively deleting that source of damage.

Reproduce the issue by creating a new build, adding a minion skill with Infernal Legion, and hovering over another support in its dropdown. Trace the preview and gem-selection entry points to see why the Main Skill changes, then verify that the preview clearly reflects removal of the current DPS source and no longer reports misleading totals.