patch 9.1.0546: vim-tiny fails on CTRL-X/CTRL-A

Problem:  vim-tiny fails on CTRL-X/CTRL-A
          (Rob Foehl, after 9.1.0172)
Solution: Move #ifdefs, so that after changing the line in del_bytes,
          the cached textlen value is invalidated

closes: #15178

Co-authored-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test28.in b/src/testdir/test28.in
new file mode 100644
index 0000000..3d5289d
--- /dev/null
+++ b/src/testdir/test28.in
@@ -0,0 +1,13 @@
+Test for using CTRL-A/CTRL-X in tiny mode
+
+STARTTEST
+/12352
+/12354
+:/^STARTHERE/+,$w! test.out
+:qa!
+ENDTEST
+
+STARTHERE
+12352
+
+12354