patch 8.2.4924: maparg() may return a string that cannot be reused

Problem:    maparg() may return a string that cannot be reused.
Solution:   use msg_outtrans_special() instead of str2special().
            (closes #10384)
diff --git a/src/option.c b/src/option.c
index 33bb641..e93c14c 100644
--- a/src/option.c
+++ b/src/option.c
@@ -4017,6 +4017,8 @@
 	    if ((char_u **)varp == &curbuf->b_p_key
 						&& **(char_u **)(varp) != NUL)
 		*stringval = vim_strsave((char_u *)"*****");
+	    else if ((char_u **)varp == &p_pt)	// 'pastetoggle'
+		*stringval = str2special_save(*(char_u **)(varp), FALSE);
 	    else
 #endif
 		*stringval = vim_strsave(*(char_u **)(varp));