patch 8.2.2594: alternate buffer added to session file even when it's hidden

Problem:    Alternate buffer added to session file even when it's hidden.
Solution:   Check the 'buflisted' option. (closes #7951)

src/session.c

@@ -401,11 +401,12 @@ put_view(
     {
 	buf_T *alt = buflist_findnr(wp->w_alt_fnum);
 
-	// Set the alternate file.
+	// Set the alternate file if the buffer is listed.
 	if ((flagp == &ssop_flags)
 		&& alt != NULL
 		&& alt->b_fname != NULL
 		&& *alt->b_fname != NUL
+		&& alt->b_p_bl
 		&& (fputs("balt ", fd) < 0
 		|| ses_fname(fd, alt, flagp, TRUE) == FAIL))
 	    return FAIL;

src/testdir/test_mksession.vim

@@ -544,6 +544,20 @@ func Test_mkview_no_balt()
   %bwipe
 endfunc
 
+func Test_mksession_no_balt()
+  edit Xtestfile1
+  edit Xtestfile2
+
+  bdelete Xtestfile1
+  mksession! Xtestview
+
+  source Xtestview
+  call assert_equal(0, buflisted('Xtestfile1'))
+
+  call delete('Xtestview')
+  %bwipe
+endfunc
+
 " Test :mkview with a file argument.
 func Test_mkview_file()
   " Create a view with line number and a fold.

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2594,
 /**/
     2593,
 /**/