Fix missing fallback argument for InitFromParams(::ModeResult)

[penelopeysm]

Closes #2607. Note that this requires TuringLang/DynamicPPL.jl#1171 to go through first. Hence I can't add a test. But once the DPPL one is done, I will add the following test, which works locally: Test added

julia> using Turing

julia> @model function f()
           x ~ Normal()
           return x + 1
       end
f (generic function with 2 methods)

julia> mapp = maximum_a_posteriori(f())
ModeResult with maximized lp of -0.92
[0.0]

julia> returned(f(), mapp)
1.0

[github-actions]

Turing.jl documentation for PR #2736 is available at:
https://TuringLang.github.io/Turing.jl/previews/PR2736/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.51%. Comparing base (4dc7ad0) to head (041d7c8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2736   +/-   ##
=======================================
  Coverage   86.51%   86.51%           
=======================================
  Files          20       20           
  Lines        1261     1261           
=======================================
  Hits         1091     1091           
  Misses        170      170           

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[sunxd3]

looks good in current state, will take another look once DPPL PR goes through