patch 8.1.0746: highlighting not updated with conceal and 'cursorline'

Problem:    Highlighting not updated with conceal and 'cursorline'. (Jason
            Franklin)
Solution:   Do not use a zero line number.  Check if 'conceallevel' is set for
            the current window.
diff --git a/src/main.c b/src/main.c
index b693800..9e23606 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1170,6 +1170,10 @@
 	    // locked, this would be a good time to handle the drop.
 	    handle_any_postponed_drop();
 #endif
+#ifdef FEAT_CONCEAL
+	    if (curwin->w_p_cole == 0)
+		conceal_update_lines = FALSE;
+#endif
 
 	    /* Trigger CursorMoved if the cursor moved. */
 	    if (!finish_op && (
@@ -1201,6 +1205,7 @@
 			|| need_cursor_line_redraw))
 	    {
 		if (conceal_old_cursor_line != conceal_new_cursor_line
+			&& conceal_old_cursor_line != 0
 			&& conceal_old_cursor_line
 						<= curbuf->b_ml.ml_line_count)
 		    redrawWinline(curwin, conceal_old_cursor_line);