Simplified passing of data to _accept

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

Author: radarhere

src/PIL/BmpImagePlugin.py

@@ -263,7 +263,7 @@ def _open(self):
         # read 14 bytes: magic number, filesize, reserved, header final offset
         head_data = self.fp.read(14)
         # choke if the file does not have the required magic bytes
-        if not _accept(head_data[0:2]):
+        if not _accept(head_data):
             raise SyntaxError("Not a BMP file")
         # read the start position of the BMP image data (u32)
         offset = i32(head_data[10:14])