initialize value; avoid compiler warning

[[Imported from SVN: r6270]]

dune/solvers/solvers/loopsolver.cc

@@ -87,7 +87,7 @@ void ::LoopSolver<VectorType, BitVectorType>::solve()
         oldSolution -= iterationStep_->getSol();
 
         double normOfCorrection;
-        double normOfError;
+        double normOfError=std::numeric_limits<double>::quiet_NaN();
         double convRate;
 
         normOfCorrection = this->errorNorm_->operator()(oldSolution);