patch 8.2.4652: leaking memory if assignment fails

Problem:    Leaking memory if assignment fails.
Solution:   Clear assigned value on failure.
diff --git a/src/version.c b/src/version.c
index fdc4ae3..843affd 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4652,
+/**/
     4651,
 /**/
     4650,
diff --git a/src/vim9execute.c b/src/vim9execute.c
index 19f5bdc..7ff2eaf 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -3098,6 +3098,7 @@
 			if (iptr->isn_type == ISN_STOREEXPORT)
 			{
 			    semsg(_(e_undefined_variable_str), name);
+			    clear_tv(STACK_TV_BOT(0));
 			    goto on_error;
 			}
 			store_var(name, STACK_TV_BOT(0));
@@ -3118,6 +3119,7 @@
 				{
 				    semsg(_(e_item_not_exported_in_script_str),
 									 name);
+				    clear_tv(STACK_TV_BOT(0));
 				    goto on_error;
 				}
 			    }