fix: change initialization of simage and gimage variables

[Jeredian]

Description

This fixes error: local variable referenced before assignment

Type of change

What kind of change does this PR introduce?

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, local variables)
• Translations
• Documentation
• Other... Please describe:

What is the current behavior?

What is the new behavior(if this is a feature change)?

No error shown

How has this been tested?

• Disable "preview" settings, or choose "FLSUN QQ-S" printer
• Slice model
• Try to save on local disk, or upload to the printer
• Error will be shown

• Tested on MacOS
• Tested on Windows

Does this PR introduce a breaking change?

• Yes
• No

Does it closes one of the existing issues?

• Yes
• No

Fixes #403

Other information

PR Checklist:

• The pull request opens from the issue/patch/feature/bugfix branch (right side) and not main branch!
• The pull request title, commit messages and code are follows our guidelines: Contribution guide
• All commits are signed-off. See How to sign-off commit
• The code changes are commented, particularly in hard-to-understand areas

[sonarcloud]

Quality Gate passed

Issues
0 New issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud