Fix stage:number suffix returning stage number of the active vessel (#3130)

Author: sug44

src/kOS/Suffixed/StageValues.cs

@@ -40,12 +40,9 @@ internal StageValues(SharedObjects shared)
 
         private void InitializeSuffixes()
         {
-            // TODO: TEST IF THIS IS BROKEN WHEN CPU VESSEL != ACTIVE VESSEL
-            // Some of these values come from StageManager, which is part of the UI and
-            // only refers to the "active vessel", while others come from shared.Vessel and
-            // thus refer to the CPU vessel.  Those aren't always the same thing:
+            // WARNING: StageManager refers to the active vessel and not the CPU vessel
 
-            AddSuffix("NUMBER", new Suffix<ScalarValue>(() => StageManager.CurrentStage));
+            AddSuffix("NUMBER", new Suffix<ScalarValue>(() => shared.Vessel.currentStage));
             AddSuffix("READY", new Suffix<BooleanValue>(() => shared.Vessel.isActiveVessel && StageManager.CanSeparate));
             AddSuffix("RESOURCES", new Suffix<ListValue<ActiveResourceValue>>(GetResourceManifest));
             AddSuffix("RESOURCESLEX", new Suffix<Lexicon>(GetResourceDictionary));