Core/Entities: handle more edge cases in IsInAir

can be done in one liner, with one math expression if I'm not mistaken, but this allows easier debugging

Author: ccrs

src/server/game/Entities/Unit/Unit.cpp

@@ -3166,7 +3166,17 @@ bool Unit::IsUnderWater() const
 
 bool Unit::IsInAir(Position const destination, float destinationFloor, bool honorHover/* = true*/) const
 {
-    return std::fabs(destination.GetPositionZ() - (honorHover ? GetHoverOffset() : 0.f) - destinationFloor) > 0.1f;
+    float z = destination.GetPositionZ();
+    if (z < destinationFloor - 0.5f) // if really bellow ground, in air (caves,...)
+        return true;
+    float hoverHeight = GetHoverOffset(); // height if currently hovering
+    if (GetTypeId() == TYPEID_UNIT) {
+        hoverHeight = ToCreature()->CanHover() ? GetFloatValue(UNIT_FIELD_HOVERHEIGHT) : 0.f; // height if could hover
+    }
+    z = destination.GetPositionZ() - (honorHover ? hoverHeight : 0.f);
+    if (z <= destinationFloor + 0.5f) // if is bellow ground or slightly above it, not in air - should hover too
+        return false;
+    return std::fabs(z - destinationFloor) > 0.5f; // if the difference is higher than tolerance level, in air (todo: this should most likely take into account unit's "size")
 }
 
 void Unit::ProcessPositionDataChanged(PositionFullTerrainStatus const& data)