patch 8.2.3471: crash when using CTRL-T after an empty search pattern

Problem:    Crash when using CTRL-T after an empty search pattern.
Solution:   Bail out when there is no previous search pattern. (closes #8953)
diff --git a/src/testdir/test_search.vim b/src/testdir/test_search.vim
index dd47f4f..bc2b3ad 100644
--- a/src/testdir/test_search.vim
+++ b/src/testdir/test_search.vim
@@ -1977,4 +1977,14 @@
   bw!
 endfunc
 
+func Test_no_last_search_pattern()
+  CheckOption incsearch
+
+  let @/ = ""
+  set incsearch
+  " this was causing a crash
+  call feedkeys("//\x14", 'xt')
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab