Don't force-trace down swimming actors (bug #5089)

CHANGELOG.md

@@ -112,6 +112,7 @@
     Bug #5074: Paralyzed actors greet the player
     Bug #5075: Enchanting cast style can be changed if there's no object
     Bug #5082: Scrolling with controller in GUI mode is broken
+    Bug #5089: Swimming/Underwater creatures only swim around ground level
     Bug #5092: NPCs with enchanted weapons play sound when out of charges
     Bug #5093: Hand to hand sound plays on knocked out enemies
     Feature #1774: Handle AvoidNode

apps/openmw/mwworld/worldimp.cpp

@@ -1401,7 +1401,7 @@ namespace MWWorld
 
         pos.z() += 20; // place slightly above. will snap down to ground with code below
 
-        if (force || !ptr.getClass().isActor() || (!isFlying(ptr) && isActorCollisionEnabled(ptr)))
+        if (force || !ptr.getClass().isActor() || (!isFlying(ptr) && !isSwimming(ptr) && isActorCollisionEnabled(ptr)))
         {
             osg::Vec3f traced = mPhysics->traceDown(ptr, pos, Constants::CellSizeInUnits);
             if (traced.z() < pos.z())