patch 8.1.0760: no proper test for using 'termencoding'

Problem:    No proper test for using 'termencoding'.
Solution:   Add a screendump test.  Fix using double width characters in a
            screendump.
diff --git a/src/version.c b/src/version.c
index c4c5969..40e4bf3 100644
--- a/src/version.c
+++ b/src/version.c
@@ -796,6 +796,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    760,
+/**/
     759,
 /**/
     758,