Make an assertion fatal

Made possible by 1e279e0c5f62ca42a9c65bf739b3f96467a04ece

dune/tectonic/myblockproblem.hh

@@ -122,14 +122,14 @@ template <class MyConvexProblemTypeTEMPLATE> class MyBlockProblem {
       localA = <Av,v>
       localb = <b - Au, v>
     */
+
     MyDirectionalConvexFunction<Dune::GlobalNonlinearity<block_size>> const psi(
         localA, localb, problem.phi, u, v);
 
     Interval<double> D;
     psi.subDiff(0, D);
-    // FIXME: this should never happen to begin with
     if (D[1] >= 0)
-      return 0.0;
+      assert(false);
 
     int bisectionsteps = 0;
     Bisection bisection(0.0, 1.0, 1e-12, true, 0);                      // TODO