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:/".

src/version.c

@@ -769,6 +769,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1028,
 /**/
     1027,
 /**/