Clean WARNING for non-void function without return

src/camel/Engine.cc

@@ -118,8 +118,8 @@ Engine::get(const std::string& key)
     else if (var=="z_reio") return  get_z_reio();
     else if (var=="H") return  get_H(z);
     else if (var=="com_distance") return  com_distance(z);
-     else if (var=="growthD") return  get_growthD(z);
-    else planck_assert(false,("key="+key+" not found in Engine::get()"));
+    else if (var=="growthD") return  get_growthD(z);
+    else { planck_assert(false,("key="+key+" not found in Engine::get()")); return -1;}
   }