Fix Monaghan-Kajtar BC (#264)

* Fix Monaghan-Kajtar BC

* Reformat

* Add comment

* Revert NHS of rectangular tank example

* Revert change in rectangular tank example

src/general/semidiscretization.jl

@@ -117,11 +117,17 @@ end
     return compact_support(system, system.boundary_model, neighbor)
 end
 
-@inline function compact_support(system, model, neighbor)
+@inline function compact_support(system, model::BoundaryModelMonaghanKajtar, neighbor)
     # Use the compact support of the fluid for solid-fluid interaction
     return compact_support(neighbor, system)
 end
 
+@inline function compact_support(system, model::BoundaryModelMonaghanKajtar,
+                                 neighbor::BoundarySPHSystem)
+    # This NHS is never used
+    return 0.0
+end
+
 @inline function compact_support(system, model::BoundaryModelDummyParticles, neighbor)
     # TODO: Monaghan-Kajtar BC are using the fluid's compact support for solid-fluid
     # interaction. Dummy particle BC use the model's compact support, which is also used