patch 8.1.1718: popup menu highlighting does not look good

Problem:    Popup menu highlighting does not look good.
Solution:   Highlight the whole window line.  Fix that sign line HL is not
            displayed in a window with a background color.
diff --git a/src/screen.c b/src/screen.c
index 5cffdf1..7998710 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -5366,6 +5366,8 @@
 			if (wp->w_p_cul && lnum == wp->w_cursor.lnum)
 			    char_attr = hl_combine_attr(char_attr,
 							    HL_ATTR(HLF_CUL));
+			else if (line_attr)
+			    char_attr = hl_combine_attr(char_attr, line_attr);
 		    }
 # endif
 		}