Could be more gracefully with bogus disconnector configuration

[laurgarn]

• Do you want to request a feature or report a bug?

In between, because it is handling a bogus situation with more explicit message.

• What is the current behavior?

When one creates a disconnector with both ends on the same bus bar section, the SLD throws

single-line-diagram-server_1    | 2022-01-25 15:47:12.927 ERROR 1 --- [p-nio-80-exec-8] o.a.c.c.C.[.[.[/].[dispatcherServlet]   : Servlet.service() for servlet [dispatcherServle
t] in context with path [] threw exception [Request processing failed; nested exception is com.powsybl.commons.PowsyblException: LegPrimaryBlock not consistent] with root cause 
single-line-diagram-server_1    | 
single-line-diagram-server_1    | com.powsybl.commons.PowsyblException: LegPrimaryBlock not consistent 
single-line-diagram-server_1    |     at com.powsybl.sld.model.LegPrimaryBlock.<init>(LegPrimaryBlock.java:43) ~[powsybl-single-line-diagram-core-2.4.0.jar:na] 

• If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem

• What is the expected behavior?

A more specific message could help requesting end figure out what is wrong.

• What is the motivation / use case for changing the behavior?

In GridSuite, no SLD is shown is such a case (and that is OK) but it is replaced by a mere message telling a web request has failed,
leaving user without a clue about what really went wrong and the trace show no clue either.

• Please tell us about your environment:
  • PowSyBl Version: ...
  • OS Version: ...

PowSyBl 4.4
Ubuntu 20.04.3 LTS

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, spectrum, etc)

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