Crash in Godot Physics when removing a rigid body connected in a constraint

[pouleyKetchoupp]

Godot version:
Master af2703c

OS/device including version:
Windows 10

Issue description:
This issue happens for both Godot Physics 2D and Godot Physics 3D. When removing a body which is still connected to another one with a joint and both are set to rigid bodies (not static or kinematic) the game crashes with no warning.

Crash callstack (it's similar for 2D and 3D):

 godot.windows.tools.64.exe!Space2DSW::get_body_angular_velocity_sleep_threshold() Line 164	C++
 godot.windows.tools.64.exe!Body2DSW::sleep_test(float p_step) Line 618	C++
 godot.windows.tools.64.exe!Step2DSW::_check_suspend(Body2DSW * p_island, float p_delta) Line 105	C++
 godot.windows.tools.64.exe!Step2DSW::step(Space2DSW * p_space, float p_delta, int p_iterations) Line 287	C++
 godot.windows.tools.64.exe!PhysicsServer2DSW::step(float p_step) Line 1240	C++
 godot.windows.tools.64.exe!PhysicsServer2DWrapMT::step(float p_step) Line 76	C++
 godot.windows.tools.64.exe!Main::iteration() Line 2491	C++

Steps to reproduce:

1. Open MRP
2. Run JointTest2D.tscn or JointTest3D.tscn
3. Observe crash

Minimal reproduction project:
JointTest.zip