patch 8.2.2142: memory leak when heredoc is not terminated

Problem:    Memory leak when heredoc is not terminated.
Solution:   Free heredoc_trimmed.
diff --git a/src/userfunc.c b/src/userfunc.c
index ccd1bd3..2d71a7f 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -3705,6 +3705,7 @@
 ret_free:
     ga_clear_strings(&argtypes);
     vim_free(skip_until);
+    vim_free(heredoc_trimmed);
     vim_free(line_to_free);
     vim_free(fudi.fd_newkey);
     if (name != name_arg)