Fix handling of squeezing in plot_shock_decomposition

The original bug in https://forum.dynare.org/t/init2shocks-does-not-work/24591 was addressed via a4e65314

We still need to address how to deal with squeezing of results that is currently addressed in plot_shock_decomposition via

try
    [i_var,nvar,index_uniques] = varlist_indices(varlist,M_.endo_names);
catch ME
    if isfield(oo_.shock_decomposition_info,'i_var')
        warning('shock decomp results for some input variable was not stored: I recompute all decompositions')
        M_ = evalin('base','M_');

Particularly loading M_ when it is an input if problematic.