Fix via dump throwing an error on sponge

sponge/src/main/java/com/viaversion/viaversion/SpongePlugin.java

@@ -213,7 +213,7 @@ public class SpongePlugin implements ViaPlatform<Player> {
                 true,
                 metadata.name().orElse("Unknown"),
                 metadata.version().toString(),
-                    plugin.instance().getClass().getCanonicalName(),
+                plugin.instance() != null ? plugin.instance().getClass().getCanonicalName() : "Unknown",
                 metadata.contributors().stream().map(PluginContributor::name).collect(Collectors.toList())
             ));
         }