fix another plexon overflow

Author: zm711

neo/rawio/plexonrawio.py

@@ -155,7 +155,9 @@ def _parse_header(self):
         if self.progress_bar:
             progress_bar.close()
 
-        self._last_timestamps = bl_header["UpperByteOf5ByteTimestamp"] * 2**32 + bl_header["TimeStamp"]
+        upper_byte_of_5_byte_timestamp = int(bl_header["UpperByteOf5ByteTimestamp"])
+        bl_header_timestamp = int(bl_header["TimeStamp"])
+        self._last_timestamps =  upper_byte_of_5_byte_timestamp * 2**32 + bl_header_timestamp
 
         # ... and finalize them in self._data_blocks
         # for a faster access depending on type (1, 4, 5)