patch 9.0.0581: adding a character for incsearch fails at end of line

Problem:    Adding a character for incsearch fails at end of line.
Solution:   Only check cursor line number.
diff --git a/src/move.c b/src/move.c
index 967dd77..8a8af9a 100644
--- a/src/move.c
+++ b/src/move.c
@@ -683,7 +683,7 @@
     void
 validate_cursor(void)
 {
-    check_cursor();
+    check_cursor_lnum();
     check_cursor_moved(curwin);
     if ((curwin->w_valid & (VALID_WCOL|VALID_WROW)) != (VALID_WCOL|VALID_WROW))
 	curs_columns(TRUE);