Fix the timeout value

[Ionys320]

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Description

When editing a monitor, the timeout default value is automatically set. While the monitor is not saved, the value previously set by the user is used (even if another value is shown in the UI). But still, the correct value wans't defined. This was caused by f059d54, which were changing the timeout when monitor type were changed.

Fixes #5337

Type of change

• Bug fix (non-breaking change which fixes an issue)
• User interface (UI)

Checklist

• My code follows the style guidelines of this project
• I ran ESLint and other linters for modified files
• I have performed a self-review of my own code and tested it
• I have commented my code, particularly in hard-to-understand areas (including JSDoc for methods)
• My changes generates no new warnings
• My code needed automated testing. I have added them (this is optional task)

[CommanderStorm]

How this is usually checked for the other defaults is that it is only set for undefined => falsy values.

For this one, changing on monitor-type change makes also sense => this impl is better