without a valid target
rB95b9680597f5 introduced code that would skip creation of GPUVertBuf
for ParticlePointCache if the keyed physics would not have a valid
target. Missing vertex buffer would lead to assert/crash.
This code is now removed (dont see a reason why this was done? afaict
2.79 also just displayed the particles without physics in this case and
this seems to be working just fine in 2.8 as well)
part of T69741
Reviewers: fclem
Maniphest Tasks: T69741
Differential Revision: https://developer.blender.org/D5781
89cc5c2bd3