Merge branch 'feature/assembleResidualInitiallyZero' into 'master'

[fvassembler] Set r=0 in the beginning of assembleResidual

See merge request !2705

dumux/multidomain/fvassembler.hh

@@ -209,6 +209,8 @@ public:
     //! assemble a residual r
     void assembleResidual(ResidualType& r, const SolutionVector& curSol)
     {
+        r = 0.0;
+
         checkAssemblerState_();
 
         // update the grid variables for the case of active caching