SampleStore Should be Able to Handle trials == 0 and trials == 1 Cleanly

[lrennels]

ERROR: MethodError: no method matching Mimi.SampleStore(::Float64, ::Nothing)
Closest candidates are:
  Mimi.SampleStore(::Vector{T}, ::Union{Nothing, Mimi.PseudoDistribution, Distributions.Distribution}) where T at /Users/lisarennels/.julia/packages/Mimi/eGQF9/src/mcs/mcs_types.jl:55
Stacktrace:
 [1] rand!(sim_inst::MonteCarloSimulationInstance)
   @ Mimi ~/.julia/packages/Mimi/eGQF9/src/mcs/montecarlo.jl:243
 [2] sample!
   @ ~/.julia/packages/Mimi/eGQF9/src/mcs/montecarlo.jl:224 [inlined]
 [3] #generate_trials!#244
   @ ~/.julia/packages/Mimi/eGQF9/src/mcs/montecarlo.jl:213 [inlined]
 [4] run(sim_def::MonteCarloSimulationDef, models::Model, samplesize::Int64; ntimesteps::Int64, trials_output_filename::String, results_output_dir::String, pre_trial_func::Nothing, post_trial_func::Nothing, scenario_func::Nothing, scenario_placement::Mimi.ScenarioLoopPlacement, scenario_args::Nothing, results_in_memory::Bool)
   @ Mimi ~/.julia/packages/Mimi/eGQF9/src/mcs/montecarlo.jl:536
 [5] run_mcs(; trials::Int64, output_dir::Nothing, save_trials::Bool, m::Model)
   @ Main.RffModel ~/JuliaProjects/RFF Model/RffModel.jl/src/main_mcs.jl:153
 [6] top-level scope
   @ REPL[13]:1