[Cleanup] Do not require 2 fixed point iterations

src/sand-wedge.cc

@@ -128,7 +128,7 @@ class FixedPointIterator {
         multigridStep, velocityMaxIterations_, velocityTolerance_,
         &velocityMatrixNorm, verbosity_, false); // absolute error
 
-    Vector previousVelocityIterate;
+    Vector previousVelocityIterate = velocityIterate;
 
     for (size_t fixedPointIteration = 1;
          fixedPointIteration <= fixedPointMaxIterations_;
@@ -152,12 +152,10 @@ class FixedPointIterator {
       velocityProblemSolver.preprocess();
       velocityProblemSolver.solve();
 
-      if (fixedPointIteration > 1) {
-        auto const velocityCorrection =
-            velocityMatrixNorm.diff(previousVelocityIterate, velocityIterate);
-        if (velocityCorrection < fixedPointTolerance_)
-          break;
-      }
+      if (velocityMatrixNorm.diff(previousVelocityIterate, velocityIterate) <
+          fixedPointTolerance_)
+        break;
+
       if (fixedPointIteration == fixedPointMaxIterations_)
         DUNE_THROW(Dune::Exception, "FPI failed to converge");