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/ex_cmds2.c b/src/ex_cmds2.c
index 7233893..4b575b4 100644
--- a/src/ex_cmds2.c
+++ b/src/ex_cmds2.c
@@ -469,15 +469,14 @@
 	}
 
 	if (win_valid(prevwin) && !prevwin->w_p_wfb)
-	{
 	    // 'winfixbuf' is set; attempt to change to a window without it.
 	    win_goto(prevwin);
-	}
 	if (curwin->w_p_wfb)
 	{
 	    // Split the window, which will be 'nowinfixbuf', and set curwin to
 	    // that
-	    win_split(0, 0);
+	    if (win_split(0, 0) == FAIL)
+		return; // error message already given
 
 	    if (curwin->w_p_wfb)
 	    {