Add back header variable

Author: tannewt

adafruit_bitmap_font/lvfontbin.py

@@ -34,6 +34,10 @@
 
 from .glyph_cache import GlyphCache
 
+# The LVGL file starts with the size of the 'head' section. It hasn't changed in five years so
+# we can treat it like a magic number.
+LVGL_HEADER_SIZE = b"\x30\x00\x00\x00"
+
 
 class LVGLFont(GlyphCache):
     """Loads glyphs from a LVGL binary font file in the given bitmap_class.