patch 8.1.0937: invalid memory access in search pattern

Problem:    Invalid memory access in search pattern. (Kuang-che Wu)
Solution:   Check for incomplete collation element. (Dominique Pelle,
            closes #3985)

src/testdir/test_regexp_latin.vim

@@ -103,6 +103,8 @@ func Test_get_equi_class()
   " Incomplete equivalence class caused invalid memory access
   s/^/[[=
   call assert_equal(1, search(getline(1)))
+  s/.*/[[.
+  call assert_equal(1, search(getline(1)))
 endfunc
 
 func Test_rex_init()