fix density calculation in analytical mode

In the analytical mode the density does not have a tail, so tail%end is
not initialised. The density is exactly zero at ψ≥1.

src/coreprofiles.f90

@@ -65,9 +65,8 @@ contains
     dens  = 0
     ddens = 0
 
-    ! Outside the tail end both density and its
-    ! derivatives are identically zero
-    if (psin >= tail%end .or. psin < 0) return
+    ! Bail out when ψ is not available
+    if (psin < 0) return
 
     if (iprof == 0) then
       ! Use the analytical model
@@ -81,6 +80,10 @@ contains
     else
       ! Use the numerical data
 
+      ! Past the tail end both density and its
+      ! derivatives are identically zero
+      if (psin >= tail%end) return
+
       if (psin < tail%start) then
         ! Use the interpolating spline when in range