patch 8.0.0405: v:progpath may become invalid after :cd

Problem:    v:progpath may become invalid after ":cd".
Solution:   Turn v:progpath into a full path if needed.
diff --git a/src/version.c b/src/version.c
index 71d22de..c4ef6ac 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    405,
+/**/
     404,
 /**/
     403,