patch 8.0.0515: ml_get errors in silent Ex mode

Problem:    ml_get errors in silent Ex mode. (Dominique Pelle)
Solution:   Clear valid flags when setting the cursor.  Set the topline when
            not in full screen mode.
diff --git a/src/move.c b/src/move.c
index 3d6d2ec..f058b73 100644
--- a/src/move.c
+++ b/src/move.c
@@ -177,11 +177,9 @@
     int		save_so = p_so;
 #endif
 
-    if (!screen_valid(TRUE))
-	return;
-
-    /* If the window height is zero just use the cursor line. */
-    if (curwin->w_height == 0)
+    /* If there is no valid screen and when the window height is zero just use
+     * the cursor line. */
+    if (!screen_valid(TRUE) || curwin->w_height == 0)
     {
 	curwin->w_topline = curwin->w_cursor.lnum;
 	curwin->w_botline = curwin->w_topline;
@@ -2592,6 +2590,7 @@
     n = (curwin->w_p_scr <= curwin->w_height) ?
 				    curwin->w_p_scr : curwin->w_height;
 
+    update_topline();
     validate_botline();
     room = curwin->w_empty_rows;
 #ifdef FEAT_DIFF