[repacker] fix fuzzer failure.

Fixes: https://oss-fuzz.com/testcase-detail/6490945267564544

src/graph/markbasepos-graph.hh

diff --git a/src/graph/markbasepos-graph.hh b/src/graph/markbasepos-graph.hh
index 5e9d5ae..e10e1cf 100644
--- a/src/graph/markbasepos-graph.hh
+++ b/src/graph/markbasepos-graph.hh
@@ -318,7 +318,9 @@
   {
     hb_vector_t<class_info_t> class_to_info;
 
-    unsigned class_count= classCount;
+    unsigned class_count = classCount;
+    if (!class_count) return class_to_info;
+
     if (!class_to_info.resize (class_count))
       return hb_vector_t<class_info_t>();
 

test/fuzzing/fonts/clusterfuzz-testcase-minimized-hb-repacker-fuzzer-6490945267564544

diff --git a/test/fuzzing/fonts/clusterfuzz-testcase-minimized-hb-repacker-fuzzer-6490945267564544 b/test/fuzzing/fonts/clusterfuzz-testcase-minimized-hb-repacker-fuzzer-6490945267564544
new file mode 100644
index 0000000..20dc975
--- /dev/null
+++ b/test/fuzzing/fonts/clusterfuzz-testcase-minimized-hb-repacker-fuzzer-6490945267564544
Binary files differ