Error Checking in EN_open is too strcit for network building by code

[LRossman]

Consider the use case where the toolkit functions are being used in some app to build a network directly by function calls. Suppose a user has created a partial network with lots of nodes of which only some have been connected by links and with no tanks/reservoirs. They then call EN_saveinpfile to save their work so they can complete their analysis at some later time. When they try to use EN_open to re-open their project again the function fails because it detects unlinked nodes and no tanks/reservoirs thus making all of their previous editing work lost to the app.

Checks on these conditions should have been made after a network is completely built and is ready to be analyzed. Other error conditions that EN_open checks for that should be postponed until a network is analyzed are invalid tank levels, invalid pump curve parameters, and an inability to open a Hydraulics file.

[eladsal]

@LRossman I think this was discussed somewhere before. Basically you need a Load function and then a Check function, right?

[LRossman]

@eladsal I think just a Check function is needed, to be called in EN_openH (or EN_openQ if no hydraulics are analyzed). EN_open can still serve as a Load function once its validity checks are removed.

[LRossman]

This issue has been successfully addressed in PR #580.