corrected pointer access in MatrixView

src/amdis/common/FieldMatVec.inc.hpp

@@ -136,7 +136,7 @@ namespace MatVec {
     {
       T operator[](size_type c) const
       {
-        assert(0 <= c && c < mat_.M());
+        assert(0 <= c && c < mat_->M());
         return c == r_ ? mat_->diagonal(r_) : T(0);
       }