Check for absence of negative probabilities in matrix

src/storm/storage/SparseMatrix.cpp

@@ -1589,6 +1589,13 @@ namespace storm {
                     return false;
                 }
             }
+            for (auto const& entry : *this) {
+                if (comparator.isConstant(entry.getValue())) {
+                    if (comparator.isLess(entry.getValue(), storm::utility::zero<ValueType>())) {
+                        return false;
+                    }
+                }
+            }
             return true;
         }