[3p3c][model] Add curly braces to switch statements

* fixes clang compiler error

dumux/porousmediumflow/3p3c/model.hh

@@ -128,35 +128,47 @@ struct ThreePThreeCModelTraits
         switch (state)
         {
             case Indices::threePhases:
+            {
                 const std::vector<std::string> s1 = {"p_g",
                                                      "S_w",
                                                      "S_n"};
                 return s1[pvIdx];
+            }
             case Indices::wPhaseOnly:
+            {
                 const std::vector<std::string> s2 = {"p_g",
                                                      "x^" + FluidSystem::componentName(FluidSystem::gCompIdx) + "_" +  FluidSystem::phaseName(FluidSystem::wPhaseIdx),
                                                      "x^" + FluidSystem::componentName(FluidSystem::nCompIdx) + "_" +  FluidSystem::phaseName(FluidSystem::wPhaseIdx)};
                 return s2[pvIdx];
+            }
             case Indices::gnPhaseOnly:
+            {
                 const std::vector<std::string> s3 = {"p_g",
                                                      "x^" + FluidSystem::componentName(FluidSystem::wCompIdx) + "_" +  FluidSystem::phaseName(FluidSystem::gPhaseIdx),
                                                      "S_n"};
                 return s3[pvIdx];
+            }
             case Indices::wnPhaseOnly:
+            {
                 const std::vector<std::string> s4 = {"p_g",
                                                      "x^" + FluidSystem::componentName(FluidSystem::gCompIdx) + "_" +  FluidSystem::phaseName(FluidSystem::wPhaseIdx),
                                                      "S_n"};
                 return s4[pvIdx];
+            }
             case Indices::gPhaseOnly:
+            {
                 const std::vector<std::string> s5 = {"p_g",
                                                      "x^" + FluidSystem::componentName(FluidSystem::wCompIdx) + "_" +  FluidSystem::phaseName(FluidSystem::gPhaseIdx),
                                                      "x^" + FluidSystem::componentName(FluidSystem::nCompIdx) + "_" +  FluidSystem::phaseName(FluidSystem::gPhaseIdx)};
                 return s5[pvIdx];
+            }
             case Indices::wgPhaseOnly:
+            {
                 const std::vector<std::string> s6 = {"p_g",
                                                      "S_w",
                                                      "x^" + FluidSystem::componentName(FluidSystem::nCompIdx) + "_" +  FluidSystem::phaseName(FluidSystem::gPhaseIdx)};
                 return s6[pvIdx];
+            }
         }
     }
 };