patch 7.4.1751

Problem:    Crash when 'tagstack' is off. (Dominique Pelle)
Solution:   Fix it. (Hirohito Higashi)

src/tag.c

@@ -200,6 +200,14 @@ do_tag(
     {
 	use_tagstack = FALSE;
 	new_tag = TRUE;
+#if defined(FEAT_WINDOWS) && defined(FEAT_QUICKFIX)
+	if (g_do_tagpreview != 0)
+	{
+	    vim_free(ptag_entry.tagname);
+	    if ((ptag_entry.tagname = vim_strsave(tag)) == NULL)
+		goto end_do_tag;
+	}
+#endif
     }
     else
     {

src/testdir/test_alot.vim

@@ -27,6 +27,7 @@ source test_sort.vim
 source test_statusline.vim
 source test_syn_attr.vim
 source test_tabline.vim
+source test_tagjump.vim
 source test_timers.vim
 source test_undolevels.vim
 source test_unlet.vim

src/version.c

@@ -748,6 +748,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1751,
 /**/
     1750,
 /**/