Ensure to use int values to determine maximum values in graphs

[sgiehl]

Description:

fixes #20357

Review

• Functional review done
• Potential edge cases thought about (behavior of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• Security review done
• Wording review done
• Code review done
• Tests were added if useful/possible
• Reviewed for breaking changes
• Developer changelog updated if needed
• Documentation added if needed
• Existing documentation updated if needed

[bx80]

• Functional review done
• Potential edge cases thought about (behavior of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• Security review done
• n/a Wording review done
• Code review done
• n/a Tests were added if useful/possible
• none Reviewed for breaking changes
• n/a Developer changelog updated if needed
• n/a Documentation added if needed
• n/a Existing documentation updated if needed