Fix generate Format tag

[tltk90]

Could solve #962

[KaiVolland]

Hey @tltk90, thanks for your contribution.

Could you add a new test with a corresponding SLD and geostyler-style?

[KaiVolland]

Are you sure the index has to be changed from [ExternalGraphic][0] to one [ExternalGraphic][1] here?

[tltk90]

Yes. if it is on [ExternalGraphic][0] the Format was ignore.

[tltk90]

@KaiVolland I think the existing tests are sufficient, I had a spelling error, that's why the tests failed earlier.
I fixed it. The test can write a SLD PointSymbolizer with ExternalGraphic

[KaiVolland]

If the tests were sufficient they should have failed before your MR 😄 . Or in other words; could you add a test that demonstrates the correct translation of a graphic with an extension?

... or just add an SLD to the issue that failed before this PR. I can add it afterwards.

[tltk90]

Sorry on the delay with the answer,
The "problem" with the tests is the Format tag is not part of the geostyler object,
and in all the tests we you need to compare sld you convert it back to geostyler object,
so you don't catch this problem.

You can see this in the test
can write a SLD 1.1 PointSymbolizer with ExternalGraphic svg
if you print the sldString before convert it back to geostyler you see the format was missing.

[KaiVolland]

Thanks for the contribution @tltk90 🙏