Include ccall :jl_generating_output in try block

[fonsp]

This guards against the situation where :jl_generating_output is removed in a future release

julia> ccall(:jl_asdfasdfasdf, Cint, ())
ERROR: could not load symbol "jl_asdfasdfasdf":
dlsym(RTLD_DEFAULT, jl_asdfasdfasdf): symbol not found
Stacktrace:
 [1] top-level scope
   @ ./REPL[1]:1

julia> try
           ccall(:jl_asdfasdfasdf, Cint, ())
       catch
           0
       end
0

[rikhuijzer]

This guards against the situation where :jl_generating_output is removed in a future release

julia> ccall(:jl_asdfasdfasdf, Cint, ())
ERROR: could not load symbol "jl_asdfasdfasdf":
dlsym(RTLD_DEFAULT, jl_asdfasdfasdf): symbol not found
Stacktrace:
 [1] top-level scope
   @ ./REPL[1]:1

julia> try
           ccall(:jl_asdfasdfasdf, Cint, ())
       catch
           0
       end
0

Ah this is of course for your goal of ensuring that Pluto can always reproduce stuff. Nice! I'll merge and register a new version as soon as the tests pass.