Improved test coverage.

src/main/java/org/orekit/gnss/metric/ntrip/NtripClient.java

...st/java/org/orekit/files/ccsds/ndm/tdm/TdmParserTest.java

...st/java/org/orekit/gnss/metric/ntrip/NtripClientTest.java

src/test/resources/ccsds/tdm/kvn/TDMExample6.txt

src/test/resources/ccsds/tdm/kvn/TDMExample8.txt

...test/resources/ccsds/tdm/xml/TDM-missing-participants.xml

src/test/resources/ccsds/tdm/xml/TDMExample6.xml

src/test/resources/ccsds/tdm/xml/TDMExample8.xml

src/test/resources/gnss/ntrip/forbidden-request.txt

src/test/resources/gnss/ntrip/missing-flags.txt

.../resources/gnss/ntrip/sourcetable-products.igs-ip.net.txt