Remote sort reset/clean broken by changes made for #1752.

[dawnmist]

The changes made for Issue #1752 breaks the ability to remove/reset a sort when remote sorting is used.

Prior to this change, clearing a sort used to work by:

• Using Table.cleanSort(), and
• Setting SortOrder = undefined, SortName = '' in the table options.

Doing this with 4.2.0 (I would assume in 4.1.5 - I just tried upgrading from 4.1.4) results in BootstrapTable throwing the error: "The type of sort field and order should be both with String or Array".

The changes made for issue #1752 do not take into account/provide any way to reset the current sort without triggering the above error. i.e. TableDataStore.setSortInfo(sortOrder, options.sortName) enforces that sortOrder must never be undefined.

[AllenFang]

@dawnmist when you got the error? call cleanSort? or set sortName and sortOrder? and are you using the remote sort right?

Regards,
Allen

[dawnmist]

Yes, using remote sorting.
Yes, occurs when Option.SortOrder = undefined and Options.SortName = ''.

This commit introduced the problem, because the function it calls validates that SortOrder must be the same type as SortName - but when there is no sort SortOrder (previously) was undefined. So the test fails and throws the Error "The type of sort field and order should be both with String or Array". 06b3560

[AllenFang]

@dawnmist I see, I think the sortName is supposed to be undefined right? i know this patch will break your program and make you feel this might be a bug. Yes, that's a problem that I didn't handle it well at before. Anyway, I'll suggest to clean the sort status by undefined in this circumstances.

A example I used it before: https://github.com/AllenFang/react-bootstrap-table/blob/master/examples/js/sort/manage-sort-external-table.js#L28-L29

Please let me know if you have any question or idea, thanks a lot !!!