patch 9.0.0101: invalid memory access in diff mode with "dp" and undo

Problem:    Invalid memory access in diff mode with "dp" and undo.
Solution:   Make sure the line number does not go below one.
diff --git a/src/version.c b/src/version.c
index 9e682a5..1241e98 100644
--- a/src/version.c
+++ b/src/version.c
@@ -736,6 +736,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    101,
+/**/
     100,
 /**/
     99,