fix: circular reference save

[a631807682]

• Do only one thing
• Non breaking API changes
• Tested

What did this pull request do?

Circular reference in model causes app freeze, should stop saveAssociations loop if relation model has been created.
close #4935

[jinzhu]

if a user has many children, and only one of them have been saved, then it won't save other children? looks like an issue?

[a631807682]

if a user has many children, and only one of them have been saved, then it won't save other children? looks like an issue?

I will create test for them.

[a631807682]

I create a test for LoadOrStoreVisitMap.
If one of them haven't been saved, then all children will be save again.
I don't know if I should change values to exclude saved children, because it looks like values is a reference and will be changed by tx.Create(values)
@jinzhu