Function pointers should not be instrumented

This was incorrectly instrumented:

This line: `fptr[idx_dst] = (*fine_volumes)(SAMRAI::pdat::CellIndex(*bi));`
Became: `fptr[idx_dst] = _FPC_CHECK_((*fine_volumes)(SAMRAI::pdat::CellIndex(* bi), ), 125, “..ineOperator.cxx”);`

Here a function pointer is assigned to an array element.

Use the reported transformation of `fptr[idx_dst] = (*fine_volumes)(SAMRAI::pdat::CellIndex(*bi));` as the reproduction case, starting with the instrumentation logic that handles function-pointer assignments. Done means this assignment is left uninstrumented without the malformed `_FPC_CHECK_` wrapper, while the issue's broader floating-point instrumentation behavior remains intact.

Written by the indexing model from the issue text.