set min-max flow rate to 0 in units

[pierre-eliep-met]

Signed-off-by: pepmts pierre-elie.personnaz@metroscope.tech

Goal

Set PositiveMassFlowRate min as 0, and NegativeMassFlowRate max to 0, to fix #282. It was not necessary to add this protection for 0 flows, since it is not used by simulation, only by compilation, and only used to show annoying and not relevant warning.

Type of change

• Bugfix (non-breaking change which fixes a bug/issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change which reorganizes code)
• Release & Version Update (when cumulative changes justify a release)
• Documentation Update

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