[instancer] bug fix

It's possible that length of all_points equals to 4 for non-empty
glyphs: a composite glyph which contains only one child glyph that is
empty.

src/OT/glyf/Glyph.hh

@@ -119,7 +119,7 @@ struct Glyph
                              hb_bytes_t &dest_bytes /* OUT */) const
   {
     GlyphHeader *glyph_header = nullptr;
-    if (!plan->pinned_at_default && type != EMPTY && all_points.length > 4)
+    if (!plan->pinned_at_default && type != EMPTY && all_points.length >= 4)
     {
       glyph_header = (GlyphHeader *) hb_calloc (1, GlyphHeader::static_size);
       if (unlikely (!glyph_header)) return false;

test/subset/data/Makefile.am

@@ -63,6 +63,7 @@ EXTRA_DIST += \
 	expected/pin_all_at_default \
 	expected/instance_no_double_free \
 	expected/mvar_full_instance \
+	expected/instance_comp_glyph_empty_child \
 	fonts \
 	profiles \
 	$(NULL)

test/subset/data/Makefile.sources

@@ -54,6 +54,7 @@ TESTS = \
 	tests/pin_all_at_default.tests \
 	tests/instance_no_double_free.tests \
 	tests/mvar_full_instance.tests \
+	tests/instance_comp_glyph_empty_child.tests \
 	$(NULL)
 
 # TODO: re-enable once colrv1 subsetting is stabilized.

test/subset/data/tests/instance_comp_glyph_empty_child.tests

@@ -0,0 +1,11 @@
+FONTS:
+RobotoMono.ttf
+
+PROFILES:
+default.txt
+
+SUBSETS:
+*
+
+INSTANCES:
+wght=700

test/subset/meson.build

@@ -56,6 +56,7 @@ tests = [
   'instance_feature_variations',
   'instance_no_double_free',
   'mvar_full_instance',
+  'instance_comp_glyph_empty_child',
 ]
 
 repack_tests = [