patch 8.0.1028: MS-Windows: viminfo uses $VIM/_viminfo if $HOME not set

Problem:    MS-Windows: viminfo uses $VIM/_viminfo if $HOME not set. (Yongwei
            Wu)
Solution:   Use vim_getenv() but check it's returning the default "C:/".
diff --git a/src/version.c b/src/version.c
index 56803bc..37afc35 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1028,
+/**/
     1027,
 /**/
     1026,