Nullify hooks::context when using RE2::Set.

Change-Id: Ic39cfa31d3346abbdbcda5baeb12ec8ec27f2f29
Reviewed-on: https://code-review.googlesource.com/c/re2/+/58510
Reviewed-by: Paul Wankadia <junyer@google.com>
diff --git a/re2/set.cc b/re2/set.cc
index c3924bf..1870566 100644
--- a/re2/set.cc
+++ b/re2/set.cc
@@ -133,6 +133,9 @@
       error_info->kind = kNotCompiled;
     return false;
   }
+#ifdef RE2_HAVE_THREAD_LOCAL
+  hooks::context = NULL;
+#endif
   bool dfa_failed = false;
   std::unique_ptr<SparseSet> matches;
   if (v != NULL) {