McStas 2.x: User-defined field functions likely not run

[willend]

When using a user-defined field-function in McStas 2.x (feature not available in 3.x) e.g. like in Test_Magnetic_Userdefined.instr, it seems that the field-function is not evaluated correctly.

(In the listede instrument example, the polarisation is not affected by the field.)

Running simulations with earlier releases, it seems we may have broken this feature somewhere between 2.4 and 2.5.

[willend]

It seems the issue is specific to that function / instrument, this one works: dataset.zip Test_Magnetic_Constant2.instr.txt