Three attack points, all after the regular calculations:
1. Prevent negative physics timestep counts. They could occur if
physics_jtter_fix is changed at runtime.
2. idle_step is not allowed to go below 1/8th of the input step.
That could happen on physics_jitter_fix changes or heavily
fluctuating performance.
3. Prevent that the idle_step modification breaks the promise
that Engine.get_physics_interpolation_fraction() is between
0 and 1 by doing more physics steps than the base system wants.
Fixes#26887
Co-authored-by: Hugo Locurcio <hugo.locurcio@hugo.pro>
Cherry-Pick from 6be702bace.
f8e62424c5
