fix bug when no convergence and backward model

(cherry picked from commit fd09b981)
9 jobs for 4.6 in 229 minutes and 39 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #17006
build_binaries

00:10:53

passed #17007
build_doc

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  Test And Pkg
passed #17010
macOS
pkg_macOS

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passed #17008
pkg_source

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passed #17009
pkg_windows

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passed #17014
test_dynare++

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passed #17011
test_matlab

00:53:43

passed #17013
test_octave

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passed #17012
test_old_matlab

01:34:09