Add braces to if-clause for clarity and to avoid dangling else warning.

dune/solvers/norms/energynorm.hh

@@ -107,10 +107,11 @@ namespace Solvers {
         //! \brief throw an exception if value is below tolerance, project to R^+ otherwise.
         static field_type checkedValue(field_type value, field_type tolerance)
         {
-            if (value < 0)
+            if (value < 0) {
                 if (value < -tolerance)
                     DUNE_THROW(Dune::RangeError, "Supplied linear operator is not positive (semi-)definite: (u,Au) = " << value);
                 else return 0.0;
+            }
             return value;
         }
     };