patch 8.0.1519: getchangelist() does not use argument as bufname()

Problem:    Getchangelist() does not use argument as bufname().
Solution:   Use get_buf_tv(). (Yegappan Lakshmanan, closes #2641)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index daef9a8..57929d6 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -4365,7 +4365,10 @@
 	return;
 
 #ifdef FEAT_JUMPLIST
-    buf = find_buffer(&argvars[0]);
+    (void)get_tv_number(&argvars[0]);	    /* issue errmsg if type error */
+    ++emsg_off;
+    buf = get_buf_tv(&argvars[0], FALSE);
+    --emsg_off;
     if (buf == NULL)
 	return;