fix: Only catch expected Exceptions in LSPEclipseUtils.getFileName(URI)

[FlorianKroiss]

LSPEclipseUtils.getFileName(URI) catches Exception, which includes a NullPointerException when Path.getFileName() returns null:

   06:46:31 WARNING [org.eclipse.lsp4e] Status WARNING: org.eclipse.lsp4e code=0 Failed to parse file name from URI file:/// java.lang.NullPointerException: Cannot invoke "java.nio.file.Path.toString()" because the return value of "java.nio.file.Path.getFileName()" is null 
  java.lang.NullPointerException: Cannot invoke "java.nio.file.Path.toString()" because the return value of "java.nio.file.Path.getFileName()" is null
  	at org.eclipse.lsp4e.LSPEclipseUtils.getFileName(LSPEclipseUtils.java:436)
  	at org.eclipse.lsp4e.test.edit.LSPEclipseUtilsTest.lambda$0(LSPEclipseUtilsTest.java:652)
  	at org.junit.jupiter.api.AssertDoesNotThrow.assertDoesNotThrow(AssertDoesNotThrow.java:76)
  	at org.junit.jupiter.api.AssertDoesNotThrow.assertDoesNotThrow(AssertDoesNotThrow.java:61)
  	at org.junit.jupiter.api.Assertions.assertDoesNotThrow(Assertions.java:3355)
  	at org.eclipse.lsp4e.test.edit.LSPEclipseUtilsTest.testReadingFileNameFromUri(LSPEclipseUtilsTest.java:652)

Catching NPEs is usually not good practice, so instead, we handle the null case explicitly. Also, we only catch expected exceptions