[subset] fix bug in parsing glyf flags.

the bytes of the flag stream were being treated as signed integers instead of unsigned as specified in the spec.

src/hb-ot-glyf-table.hh

@@ -509,8 +509,8 @@ struct glyf
       const Glyph trim_padding () const
       {
 	/* based on FontTools _g_l_y_f.py::trim */
-	const char *glyph = bytes.arrayZ;
-	const char *glyph_end = glyph + bytes.length;
+	const uint8_t *glyph = (uint8_t*) bytes.arrayZ;
+	const uint8_t *glyph_end = glyph + bytes.length;
 	/* simple glyph w/contours, possibly trimmable */
 	glyph += instruction_len_offset ();
 

test/subset/data/Makefile.am

@@ -9,6 +9,7 @@ EXTRA_DIST += \
 	$(TESTS) \
 	expected/basics \
 	expected/full-font \
+	expected/glyf_bug_3131 \
 	expected/cff-full-font \
 	expected/japanese \
 	expected/cff-japanese \

test/subset/data/Makefile.sources

@@ -9,6 +9,7 @@ TESTS = \
 	tests/colr.tests \
 	tests/colr_with_components.tests \
 	tests/full-font.tests \
+	tests/glyf_bug_3131.tests \
 	tests/japanese.tests \
 	tests/layout.context.tests \
 	tests/layout.gdef-attachlist.tests \

test/subset/data/tests/glyf_bug_3131.tests

@@ -0,0 +1,11 @@
+# Tests for https://github.com/harfbuzz/harfbuzz/issues/3131
+FONTS:
+glyf_bug_3131.ttf
+
+PROFILES:
+drop-hints-retain-gids.txt
+retain-gids.txt
+
+SUBSETS:
+cdeopqr
+*

test/subset/meson.build

@@ -5,6 +5,7 @@ tests = [
   'japanese',
   'cff-japanese',
   'cff.notoserifmyanmar',
+  'glyf_bug_3131',
   'layout',
   'layout.gpos',
   'layout.gpos2',