Force-enable hasWater() for exterior cells (Fixes #3222)

apps/openmw/mwworld/worldimp.cpp

@@ -2039,7 +2039,7 @@ namespace MWWorld
 
     bool World::isUnderwater(const MWWorld::CellStore* cell, const osg::Vec3f &pos) const
     {
-        if (!(cell->getCell()->mData.mFlags & ESM::Cell::HasWater)) {
+        if (!(cell->getCell()->hasWater())) {
             return false;
         }
         return pos.z() < cell->getWaterLevel();

components/esm/loadcell.hpp

@@ -141,7 +141,7 @@ struct Cell
 
   bool hasWater() const
   {
-      return (mData.mFlags&HasWater) != 0;
+      return ((mData.mFlags&HasWater) != 0) || isExterior();
   }
 
   // Restore the given reader to the stored position. Will try to open