patch 9.0.0341: mapset() does not restore <Nop> mapping properly

Problem:    mapset() does not restore <Nop> mapping properly.
Solution:   Use an empty string for <Nop>. (closes #11022)
diff --git a/src/version.c b/src/version.c
index d886882..2db1aa6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -708,6 +708,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    341,
+/**/
     340,
 /**/
     339,