patch 9.0.0047: using freed memory with recursive substitute

Problem:    Using freed memory with recursive substitute.
Solution:   Always make a copy for reg_prev_sub.
diff --git a/src/version.c b/src/version.c
index de8e968..2d917a8 100644
--- a/src/version.c
+++ b/src/version.c
@@ -736,6 +736,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    47,
+/**/
     46,
 /**/
     45,