patch 9.0.0683: cannot specify a time for :echowindow

Problem:    Cannot specify a time for :echowindow.
Solution:   A count can be used to specify the display time. Add
            popup_findecho().
diff --git a/src/testdir/dumps/Test_echowindow_9.dump b/src/testdir/dumps/Test_echowindow_9.dump
new file mode 100644
index 0000000..2efdef0
--- /dev/null
+++ b/src/testdir/dumps/Test_echowindow_9.dump
@@ -0,0 +1,8 @@
+| +8#0000001#e0e0e08|+| |[|N|o| |N|a|m|e|]| | +2#0000000#ffffff0|[|N|o| |N|a|m|e|]| | +1&&@49|X+8#0000001#e0e0e08
+> +0#0000000#ffffff0@74
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|~| @73
+|:+0#0000000&|c|a|l@1| |H|i|d|e|W|i|n|(|)| @59
+@57|0|,|0|-|1| @8|A|l@1|