patch 9.1.1378: sign without text overwrites number option

Problem:  When 'signcolumn' is set to `number` but a line has a sign
          without text, the line number disappears (finite-state-machine)
Solution: Verify that a sign actually contains text before rendering the
          line number (glepnir)

fixes: #17169
closes: #17282

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/drawline.c b/src/drawline.c
index a14dd90..57ee9a5 100644
--- a/src/drawline.c
+++ b/src/drawline.c
@@ -388,7 +388,8 @@
 	// If 'signcolumn' is set to 'number' and a sign is present
 	// in 'lnum', then display the sign instead of the line
 	// number.
-	if ((*wp->w_p_scl == 'n' && *(wp->w_p_scl + 1) == 'u') && sign_present)
+	if ((*wp->w_p_scl == 'n' && *(wp->w_p_scl + 1) == 'u') && sign_present
+		&& wlv->sattr.sat_text != NULL)
 	    get_sign_display_info(TRUE, wp, wlv);
 	else
 #endif