Stacktrace scrubbing in Test can error

[KristofferC]

From a PkgEval run:

  MethodError: no method matching getindex(::Ptr{Nothing}, ::Int64)
  Stacktrace:
   [1] scrub_exc_stack(::Array{Union{Ptr{Nothing}, Base.InterpreterIP},1}) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.2/Test/src/Test.jl:64
   [2] Test.Error(::Symbol, ::Expr, ::ProcessFailedException, ::Array{Union{Ptr{Nothing}, Base.InterpreterIP},1}, ::LineNumberNode) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.2/Test/src/Test.jl:152
   [3] top-level scope at /root/.julia/packages/RemoteFiles/2Wddl/test/runtests.jl:56
   [4] top-level scope at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.2/Test/src/Test.jl:1113
   [5] top-level scope at /root/.julia/packages/RemoteFiles/2Wddl/test/runtests.jl:10
   [6] top-level scope at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.2/Test/src/Test.jl:1113
   [7] top-level scope at /root/.julia/packages/RemoteFiles/2Wddl/test/runtests.jl:9
   [8] include at ./boot.jl:328 [inlined]
   [9] include_relative(::Module, ::String) at ./loading.jl:1094
   [10] include(::Module, ::String) at ./Base.jl:31
   [11] include(::String) at ./client.jl:431
   [12] top-level scope at none:5
   [13] eval(::Module, ::Any) at ./boot.jl:330
   [14] exec_options(::Base.JLOptions) at ./client.jl:271
   [15] _start() at ./client.jl:464
  caused by [exception 1]