patch 8.1.0364: compiler warning in xdiff code

Problem:    Compiler warning in xdiff code. (Yegappan Lakshmanan)
Solution:   Initialize directly.
diff --git a/src/xdiff/README.txt b/src/xdiff/README.txt
index f77893d..1afe740 100644
--- a/src/xdiff/README.txt
+++ b/src/xdiff/README.txt
@@ -11,4 +11,6 @@
 The code is distributed under the GNU LGPL license.  It is included in the
 COPYING file.
 
+Changes in these files were made to avoid compiler warnings.
+
 The first work for including xdiff in Vim was done by Christian Brabandt.