patch 8.1.2336: when an expr mapping moves the cursor it is not restored

Problem:    When an expr mapping moves the cursor it is not restored.
Solution:   Position the cursor after an expr mapping. (closes #5256)
diff --git a/src/getchar.c b/src/getchar.c
index 475ee7e..b086126 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -2594,6 +2594,8 @@
 	{
 	    int save_vgetc_busy = vgetc_busy;
 	    int save_may_garbage_collect = may_garbage_collect;
+	    int was_screen_col = screen_cur_col;
+	    int was_screen_row = screen_cur_row;
 
 	    vgetc_busy = 0;
 	    may_garbage_collect = FALSE;
@@ -2602,6 +2604,11 @@
 	    save_m_str = vim_strsave(mp->m_str);
 	    map_str = eval_map_expr(save_m_str, NUL);
 
+	    // The mapping may do anything, but we expect it to take care of
+	    // redrawing.  Do put the cursor back where it was.
+	    windgoto(was_screen_row, was_screen_col);
+	    out_flush();
+
 	    vgetc_busy = save_vgetc_busy;
 	    may_garbage_collect = save_may_garbage_collect;
 	}