patch 8.1.1983: compiler nags for uninitialized variable and unused function

Problem:    Compiler nags for uninitialized variable and unused function.
Solution:   Add unnecessary initialization.  Move function inside #ifdef.
diff --git a/src/memline.c b/src/memline.c
index b6f0300..08a99f7 100644
--- a/src/memline.c
+++ b/src/memline.c
@@ -2716,7 +2716,7 @@
     int		count;
     int		n;
     char_u	*props;
-    int		new_len;
+    int		new_len = 0;  // init for gcc
     char_u	*new_line;
     textprop_T	prop;