Merge pull request #1388 from h-mayorquin/add_is_parsed_flag

Add `is_header_parsed` flag to quickly check if header information is available in `BaseRawIO`

Author: samuelgarcia

neo/rawio/baserawio.py

@@ -162,6 +162,7 @@ def __init__(self, use_cache: bool = False, cache_path: str = 'same_as_resource'
             self._cache = None
 
         self.header = None
+        self.is_header_parsed = False
 
     def parse_header(self):
         """
@@ -178,6 +179,7 @@ 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"""