fix rosbag::View::iterator copy assignment operator

the compiler-generated copy assignment operator did lead to segfault and
memory leaks.

test/test_rosbag_storage/src/create_and_iterate_bag.cpp

@@ -29,6 +29,39 @@ void create_test_bag(const std::string &filename)
 
 const char* bag_filename = "/tmp/rosbag_storage_create_and_iterate_bag.bag";
 
+TEST(rosbag_storage, iterator_copy_constructor)
+{
+  // copy ctor
+  rosbag::Bag bag;
+  bag.open(bag_filename, rosbag::bagmode::Read);
+  rosbag::View view(bag, rosbag::TopicQuery("numbers"));
+  rosbag::View::const_iterator it0 = view.begin();
+  EXPECT_EQ(42, it0->instantiate<std_msgs::Int32>()->data);
+  rosbag::View::const_iterator it1(it0);
+  EXPECT_EQ(it0, it1);
+  EXPECT_EQ(42, it1->instantiate<std_msgs::Int32>()->data);
+  ++it1;
+  EXPECT_NE(it0, it1);
+  EXPECT_EQ(42, it0->instantiate<std_msgs::Int32>()->data);
+}
+
+TEST(rosbag_storage, iterator_copy_assignment)
+{
+  // copy assignment
+  rosbag::Bag bag;
+  bag.open(bag_filename, rosbag::bagmode::Read);
+  rosbag::View view(bag, rosbag::TopicQuery("numbers"));
+  rosbag::View::const_iterator it0 = view.begin();
+  EXPECT_EQ(42, it0->instantiate<std_msgs::Int32>()->data);
+  rosbag::View::const_iterator it1;
+  it1 = it0;
+  EXPECT_EQ(it0, it1);
+  EXPECT_EQ(42, it1->instantiate<std_msgs::Int32>()->data);
+  ++it1;
+  EXPECT_NE(it0, it1);
+  EXPECT_EQ(42, it0->instantiate<std_msgs::Int32>()->data);
+}
+
 TEST(rosbag_storage, iterate_bag)
 {
   rosbag::Bag bag;

tools/rosbag_storage/include/rosbag/view.h

@@ -63,6 +63,7 @@ class ROSBAG_DECL View
     {
     public:
         iterator(iterator const& i);
+        iterator &operator=(iterator const& i);
         iterator();
         ~iterator();
 

tools/rosbag_storage/src/view.cpp

@@ -59,6 +59,19 @@ View::iterator::iterator(View* view, bool end) : view_(view), view_revision_(0),
 
 View::iterator::iterator(const iterator& i) : view_(i.view_), iters_(i.iters_), view_revision_(i.view_revision_), message_instance_(NULL) { }
 
+View::iterator &View::iterator::operator=(iterator const& i) {
+    if (this != &i) {
+        view_ = i.view_;
+        iters_ = i.iters_;
+        view_revision_ = i.view_revision_;
+        if (message_instance_ != NULL) {
+            delete message_instance_;
+            message_instance_ = NULL;
+        }
+    }
+    return *this;
+}
+
 void View::iterator::populate() {
     assert(view_ != NULL);