Fixed corrupted messages when reopening a rosbag with a different file

* Bag::decompressed_chunk_ was not reset in close(). decompressed_chunk_
stores the offset (within the file) of the compressed chunk whose
decompressed content is currently stored in decompress_buffer_. Since it
wasn't reset in close(), if the offset is the same as that of the first
chunk in the file opened next, Bag::decompressChunk() assumed that
it had already decompressed that chunk in the new file and just returned.
As a result, some member functions of Bag worked on the decompressed
chunk of the old bag.
* Cleaned up more state in Bag::close() and ChunkedFile::close()

tools/rosbag_storage/src/bag.cpp

@@ -180,6 +180,8 @@ void Bag::close() {
     chunks_.clear();
     connection_indexes_.clear();
     curr_chunk_connection_indexes_.clear();
+
+    init();
 }
 
 void Bag::closeWrite() {

tools/rosbag_storage/src/chunked_file.cpp

@@ -148,6 +148,8 @@ void ChunkedFile::close() {
     filename_.clear();
 
     clearUnused();
+    offset_ = 0;
+    compressed_in_ = 0;
 }
 
 // Read/write modes