Fix subset fuzzer timeout. (#6019)

https://oss-fuzz.com/testcase-detail/5440786836815872

test/fuzzing/hb-subset-fuzzer.cc

diff --git a/test/fuzzing/hb-subset-fuzzer.cc b/test/fuzzing/hb-subset-fuzzer.cc
index fceeb61..d19c5ee 100644
--- a/test/fuzzing/hb-subset-fuzzer.cc
+++ b/test/fuzzing/hb-subset-fuzzer.cc
@@ -68,6 +68,11 @@
     if (finish < start)
       return false;
 
+    if (finish - start > 5000) {
+      // Prevent fuzzer timeouts by rejecting large ranges.
+      return false;
+    }
+
     if (is_add)
       hb_set_add_range (set, start, finish);
     else