Ignore missing font in fontchain_linter.py

It is totally valid if the font is missing even if the font is listed in
fonts.xml. Android Watch has less fonts and OEM vendor may reduce the
font files.

Bug: 72159040
Test: m fontchain_lint
Change-Id: I22bdf7bfeb6d80a2a338ebf7536c8eaf193b03c5

tools/fonts/fontchain_linter.py

@@ -270,6 +270,9 @@ def parse_fonts_xml(fonts_xml_path):
             if index:
                 index = int(index)
 
+            if not path.exists(path.join(_fonts_dir, font_file)):
+                continue # Missing font is a valid case. Just ignore the missing font files.
+
             record = FontRecord(
                 name,
                 frozenset(scripts),