* Fix a crash on loading a 3MF with empty project settings
opt_float() dereferences what option<>() returns without checking it, and
option<>() is called with create = false. Three CLI sites read printable_height
that way, so a 3mf whose Metadata/project_settings.config holds an empty object
takes the CLI down with a null dereference. Both models shipped in
resources/handy_models are such files, so `--info` on either of them segfaults.
Guard the three reads the way the neighbouring reads of
extruder_clearance_height_to_rod and friends already are. All three target
variables are initialised to 0 and the consumer tests for > 0, so an absent
setting already had a defined meaning and nothing changes for a project that
carries the setting.
* Add a CLI regression test for a project with empty settings
Runs --info over a copy of a shipped model whose Metadata/project_settings.config
has been rewritten to an empty object, so the test keeps covering the crash no
matter what settings the shipped models carry later.
Verified both ways: the test passes against this branch and fails with a
segmentation fault against a build without the guards.
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Co-authored-by: Rodrigo Faselli <162915171+RF47@users.noreply.github.com>
