Disallow setting 'ambiwidth' to "double" when 'listchars' or 'fillchars'
contains a character that would become double width.
diff --git a/src/option.c b/src/option.c
index fc38453..b137fa4 100644
--- a/src/option.c
+++ b/src/option.c
@@ -5745,6 +5745,12 @@
     {
 	if (check_opt_strings(p_ambw, p_ambw_values, FALSE) != OK)
 	    errmsg = e_invarg;
+	else if (set_chars_option(&p_lcs) != NULL)
+	    errmsg = (char_u *)_("E834: Conflicts with value of 'listchars'");
+# if defined(FEAT_WINDOWS) || defined(FEAT_FOLDING)
+	else if (set_chars_option(&p_fcs) != NULL)
+	    errmsg = (char_u *)_("E835: Conflicts with value of 'fillchars'");
+# endif
     }
 #endif