Fix NPE when adding new aux group

[Siedlerchr]

Fixes #10350

Init viewModel in initializing method, not in ctor as injected are not yet present in ctor

Mandatory checks

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
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[koppor]

I get following exception - related?

ERROR: Error while watching for changes: java.lang.NumberFormatException: For input string: "C:/git-repositories/koppor/tugboat2023-jabref/tb137kopp-jabref.aux"
        at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:67)
        at java.base/java.lang.Integer.parseInt(Integer.java:665)
        at java.base/java.lang.Integer.parseInt(Integer.java:781)
        at [email protected]/org.jabref.logic.importer.util.GroupsParser.texGroupFromString(GroupsParser.java:129)

[Siedlerchr]

I get following exception - related?

ERROR: Error while watching for changes: java.lang.NumberFormatException: For input string: "C:/git-repositories/koppor/tugboat2023-jabref/tb137kopp-jabref.aux"
        at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:67)
        at java.base/java.lang.Integer.parseInt(Integer.java:665)
        at java.base/java.lang.Integer.parseInt(Integer.java:781)
        at [email protected]/org.jabref.logic.importer.util.GroupsParser.texGroupFromString(GroupsParser.java:129)

#9776