If an emergency pos is required for a new root agent, correctly preserve the z co-ord instead of accidentally resetting the incorrect x co-ord

This is a one-liner.  It has already been addressed in master and 0.7-post-fixes in a more extensive way

OpenSim/Region/Framework/Scenes/ScenePresence.cs

@@ -839,7 +839,7 @@ namespace OpenSim.Region.Framework.Scenes
                     if (!(pos.Y < 0))
                         emergencyPos.Y = pos.Y;
                     if (!(pos.Z < 0))
-                        emergencyPos.X = pos.X;
+                        emergencyPos.Z = pos.Z;
                 }
                 if (pos.Y < 0)
                 {