fix: fix possible StackOverflowErrors for remake_buffer & InitializationProblems

For `InitializationProblem`s `state_values(prob)` can return `nothing`,
so calls like `remake_buffer(prob, state_values(prob), keys(u0), values(u0))`
would lead to `StackOverflowError`s due to the fallback for the deprecated `Dict` method.
This can crash julia if depwarns are enabled.

Author: SebastianM-C

src/remake.jl

@@ -55,6 +55,8 @@ function remake_buffer(sys, oldbuffer::AbstractArray, idxs, vals)
     return newbuffer
 end
 
+remake_buffer(sys, ::Nothing, idxs, vals) = nothing
+
 function remake_buffer(sys, oldbuffer, idxs, vals)
     remake_buffer(sys, oldbuffer, Dict(idxs .=> vals))
 end

test/remake_test.jl

@@ -71,3 +71,5 @@ for (buf, newbuf, idxs, vals) in [
     @test newbuf == _newbuf # test values
     @test typeof(newbuf) == typeof(_newbuf) # ensure appropriate type
 end
+
+@test isnothing(remake_buffer(sys, nothing, [], []))