TopoSort() fix

Hi Hackers,

I think I found an issue in the TopoSort() function.

As the comments say,

/* .....
* ...... If there are any other processes
* in the same lock group on the queue, set their number of
* beforeConstraints to -1 to indicate that they should be
emitted
* with their groupmates rather than considered separately.
*/

If the line "break;" exists, there is no chance to set beforeConstraints to
-1 for other processes in the same lock group.

So, I think we need delete the line "break;" . See the patch.

I just took a look, and I found all the following versions have this line .

postgresql-12beta2, postgresql-12beta1, postgresql-11.4,
postgresql-11.3,postgresql-11.0,
postgresql-10.9,postgresql-10.5, postgresql-10.0

Thanks,
Ruihai