patch 8.2.1709: Vim9: memory leak when using multiple closures

Problem:    Vim9: memory leak when using multiple closures.
Solution:   Free the partial.
diff --git a/src/vim9execute.c b/src/vim9execute.c
index 5fe5878..e4ccaaa 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -1830,6 +1830,7 @@
 			    // TODO: use a garray_T on ectx.
 			    SOURCING_LNUM = iptr->isn_lnum;
 			    emsg("Multiple closures not supported yet");
+			    vim_free(pt);
 			    goto failed;
 			}
 			tv->v_type = VAR_PARTIAL;