Add return values to private mjJCJoint methods.

PiperOrigin-RevId: 661438758
Change-Id: I08a77eb878703610ead526040d86f3f3fccb080b

src/user/user_objects.cc

@@ -1789,6 +1789,7 @@ int mjCJoint::nq(mjtJoint joint_type) {
     case mjJNT_HINGE:
       return 1;
   }
+  return 1;
 }
 
 
@@ -1803,6 +1804,7 @@ int mjCJoint::nv(mjtJoint joint_type) {
     case mjJNT_HINGE:
       return 1;
   }
+  return 1;
 }