Fix memory leak in regexp grapheme clusters

[Bug #20161]

The cc->mbuf gets overwritten, so we need to free it to not leak memory.

For example:

    str = "hello world".encode(Encoding::UTF_32LE)

    10.times do
      1_000.times do
        str.grapheme_clusters
      end

      puts `ps -o rss= -p #{$$}`
    end

Before:

    15536
    15760
    15920
    16144
    16304
    16480
    16640
    16784
    17008
    17280

After:

    15584
    15584
    15760
    15824
    15888
    15888
    15888
    15888
    16048
    16112

1 files changed, 2 insertions, 1 deletions

diff --git a/regparse.c b/regparse.c
index 1ce15da8f5..57ecd78dee 100644
--- a/regparse.c
+++ b/regparse.c
@@ -6105,7 +6105,8 @@ node_extended_grapheme_cluster(Node** np, ScanEnv* env)
           R_ERR(add_code_range(&(cc->mbuf), env, 0x000A, 0x000A)); /* CR */
           R_ERR(add_code_range(&(cc->mbuf), env, 0x000D, 0x000D)); /* LF */
           R_ERR(not_code_range_buf(env->enc, cc->mbuf, &inverted_buf, env));
-          cc->mbuf = inverted_buf; /* TODO: check what to do with buffer before inversion */
+          bbuf_free(cc->mbuf);
+          cc->mbuf = inverted_buf;
 
           env->warnings_flag &= dup_not_warned; /* TODO: fix false warning */
         }