MAVExplorer - blank figure when condition is set

MAVExplorer shows an empty graph when the variable in the condition is not present in graph command.
I set condition with:
`set condition GPS2.Spd>5`

When I try this:
`graph BARO.Alt GPS2.Spd>5`, it works:
When I try this:
`graph BARO.Alt`, it doesn't:

I've tried with different files and different variables.
I use Ubuntu on WSL2.

Reproduce the issue in MAVExplorer using `set condition GPS2.Spd>5`, then compare `graph BARO.Alt GPS2.Spd>5` with `graph BARO.Alt`. Trace the graph and condition command entry points to find why omitting the condition variable produces an empty figure. Done means `graph BARO.Alt` still renders while the condition remains active.

Written by the indexing model from the issue text.