add is header parsed

Author: h-mayorquin

neo/rawio/baserawio.py

@@ -161,6 +161,7 @@ def __init__(self, use_cache=False, cache_path='same_as_resource', **kargs):
             self._cache = None
 
         self.header = None
+        self.is_header_parsed = False
 
     def parse_header(self):
         """
@@ -177,6 +178,7 @@ def parse_header(self):
         """
         self._parse_header()
         self._check_stream_signal_channel_characteristics()
+        self.is_header_parsed = True
 
     def source_name(self):
         """Return fancy name of file source"""