patch 9.0.0873: using freed memory when executing mapclear at more prompt

Problem:    Using freed memory when executing mapclear at the more prompt.
Solution:   Do not clear mappings while listing them. (closes #11438)
diff --git a/src/version.c b/src/version.c
index e8a1fa8..5b4e34e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    873,
+/**/
     872,
 /**/
     871,