patch 8.2.1860: Vim9: memory leak when throwing empty string

Problem:    Vim9: memory leak when throwing empty string.
Solution:   Free the empty string.
diff --git a/src/version.c b/src/version.c
index 342ad7c..7720998 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1860,
+/**/
     1859,
 /**/
     1858,
diff --git a/src/vim9execute.c b/src/vim9execute.c
index 31b67d1..673bf91 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -2094,6 +2094,7 @@
 		if (tv->vval.v_string == NULL
 				       || *skipwhite(tv->vval.v_string) == NUL)
 		{
+		    vim_free(tv->vval.v_string);
 		    emsg(_(e_throw_with_empty_string));
 		    goto failed;
 		}