patch 9.0.0579: using freed memory when 'tagfunc' wipes out buffer

Problem:    Using freed memory when 'tagfunc' wipes out buffer that holds
            'complete'.
Solution:   Make a copy of the option.  Make sure cursor position is valid.

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    579,
 /**/
     578,
 /**/