patch 8.1.1932: ml_get errors after using append()

Problem:    Ml_get errors after using append(). (Alex Genco)
Solution:   Do not update the cursor twice. (closes #1737)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 498e87f..882bf09 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -1440,8 +1440,14 @@
 	tabpage_T   *tp;
 
 	appended_lines_mark(append_lnum, added);
+
+	// Only adjust the cursor for buffers other than the current, unless it
+	// is the current window.  For curbuf and other windows it has been
+	// done in mark_adjust_internal().
 	FOR_ALL_TAB_WINDOWS(tp, wp)
-	    if (wp->w_buffer == buf && wp->w_cursor.lnum > append_lnum)
+	    if (wp->w_buffer == buf
+		    && (wp->w_buffer != curbuf || wp == curwin)
+		    && wp->w_cursor.lnum > append_lnum)
 		wp->w_cursor.lnum += added;
 	check_cursor_col();
 	update_topline();