State territory — Parts of — Rivers — Multi-national rivers — Navigation — Collision in Ems Estuary — Claim of Dutch State for costs of removing wreck — Jurisdiction of Dutch courts — EEC Convention on Jurisdiction and Enforcement of Judgments in Civil and Commercial Matters, 1968, Article 5(3) — Territorial status of Ems Estuary — Whether collision to be deemed to have occurred in Dutch territory — Ems-Dollard Treaty, 1960, Article 32 — The law of the Netherlands