patch 9.1.1159: $MYVIMDIR may not always be set

Problem:  $MYVIMDIR may not always be set (after 9.1.0718)
          (sandwm)
Solution: always set $MYVIMDIR to first item in runtimepath
          (except when using --clean), update it when changing &rtp

fixes: #16609
closes: #16709

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index 3b61cdd..f29e1f3 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1159,
+/**/
     1158,
 /**/
     1157,