patch 8.2.2340: win_execute() unexpectedly returns number zero when failing

Problem:    win_execute() unexpectedly returns number zero when failing.
Solution:   Return an empty string. (closes #7665)
diff --git a/src/version.c b/src/version.c
index fe41ec2..24462a0 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2340,
+/**/
     2339,
 /**/
     2338,