patch 9.1.0152: Coverity complains about ignoring return value

Problem:  Coverity complains about ignoring return value of win_split()
          (after v9.1.150)
Solution: Check if win_split() failed, add winfixbuf.res to Makefile
diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index d365dfc..c4403e6 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -558,6 +558,7 @@
 	test_window_cmd.res \
 	test_window_id.res \
 	test_windows_home.res \
+	test_winfixbuf.res \
 	test_wordcount.res \
 	test_writefile.res \
 	test_xxd.res \
diff --git a/src/testdir/test_winfixbuf.vim b/src/testdir/test_winfixbuf.vim
index 8a1862c..edbe2c8 100644
--- a/src/testdir/test_winfixbuf.vim
+++ b/src/testdir/test_winfixbuf.vim
@@ -3248,4 +3248,15 @@
   augroup! QfChanged
 endfunc
 
+func Test_bufdo_splitwin_fails()
+  call s:reset_all_buffers()
+  let other = s:make_buffer_pairs()
+  " Make sure there is not enough room to
+  " split the winfixedbuf window
+  let &winheight=&lines
+  let &winminheight=&lines-2
+  call assert_fails(':bufdo echo 1', 'E36:')
+  set winminheight&vim winheight&vim
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab