patch 8.0.0575: using freed memory when resetting 'indentexpr'

Problem:    Using freed memory when resetting 'indentexpr' while evaluating
            it. (Dominique Pelle)
Solution:   Make a copy of 'indentexpr'.

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    575,
 /**/
     574,
 /**/