[subset] inputSequence could be empty, change the sanity check

src/hb-ot-layout-gsubgpos.hh

@@ -1642,9 +1642,8 @@ struct Rule
 	       const hb_map_t *klass_map = nullptr) const
   {
     TRACE_SUBSET (this);
-
-    const hb_array_t<const HBUINT16> input = inputZ.as_array ((inputCount ? inputCount - 1 : 0));
-    if (!input.length) return_trace (false);
+    if (unlikely (!inputCount)) return_trace (false);
+    const hb_array_t<const HBUINT16> input = inputZ.as_array (inputCount - 1);
 
     const hb_map_t *mapping = klass_map == nullptr ? c->plan->glyph_map : klass_map;
     if (!hb_all (input, mapping)) return_trace (false);

test/subset/data/Makefile.am

@@ -33,6 +33,7 @@ EXTRA_DIST += \
 	expected/layout.gdef \
 	expected/layout.gdef.glyphset \
 	expected/layout.context \
+	expected/layout.context_format2 \
 	expected/layout.gdef-varstore \
 	expected/layout.gdef-attachlist \
 	expected/layout.notonastaliqurdu \

test/subset/data/Makefile.sources

@@ -13,6 +13,7 @@ TESTS = \
 	tests/glyf_bug_3131.tests \
 	tests/japanese.tests \
 	tests/layout.context.tests \
+	tests/layout.context_format2.tests \
 	tests/layout.gdef-attachlist.tests \
 	tests/layout.gdef-varstore.tests \
 	tests/layout.gdef.tests \

test/subset/data/tests/layout.context_format2.tests

@@ -0,0 +1,9 @@
+FONTS:
+NotoSansNewa-Regular.ttf
+
+PROFILES:
+layout-test.txt
+layout-test-retain-gids.txt
+
+SUBSETS:
+*

test/subset/meson.build

@@ -25,6 +25,7 @@ tests = [
   'layout.gdef.glyphset',
   'layout.khmer',
   'layout.context',
+  'layout.context_format2',
   'layout.gdef-varstore',
   'layout.gdef-attachlist',
   'layout.notonastaliqurdu',