patch 8.0.0685: when conversion fails written file may be truncated

Problem:    When making backups is disabled and conversion with iconv fails
            the written file is truncated. (Luo Chen)
Solution:   First try converting the file and write the file only when it did
            not fail. (partly by Christian Brabandt)
diff --git a/src/version.c b/src/version.c
index 48c62a4..d595256 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    685,
+/**/
     684,
 /**/
     683,