EchoService.class will lose if the 'types' not null

[Augustvic]

What is the purpose of the change

修正 2.6.x 版本中， AbstractProxyFactory 类的 getProxy(Invoker invoker, boolean generic) 函数的一个小问题

Brief changelog

按照既定的逻辑，interfaces 数组的前两个位置应该放的是接口类和 EchoService 类，也就是说 type 应该从第三个位置即 interfaces[2] 开始放，但是此处是从 interfaces[1] 开始放的。如果 types 不为 null，EchoService.class 将会被意外覆盖。

Verifying this change

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[codecov-io]

Codecov Report

Merging #5860 into 2.6.x will decrease coverage by 0.05%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##              2.6.x    #5860      +/-   ##
============================================
- Coverage     47.46%   47.41%   -0.06%     
+ Complexity     4608     4430     -178     
============================================
  Files           577      566      -11     
  Lines         26509    25214    -1295     
  Branches       4691     4463     -228     
============================================
- Hits          12582    11954     -628     
+ Misses        12009    11418     -591     
+ Partials       1918     1842      -76

Impacted Files	Coverage Δ	Complexity Δ
.../alibaba/dubbo/rpc/proxy/AbstractProxyFactory.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...onfig/spring/extension/SpringExtensionFactory.java	75.67% <0%> (-8.11%)	9% <0%> (ø)
...a/dubbo/remoting/transport/netty/NettyChannel.java	61.25% <0%> (-5%)	20% <0%> (-1%)
...ubbo/rpc/protocol/dubbo/ChannelWrappedInvoker.java	37.5% <0%> (-4.17%)	3% <0%> (ø)
...ba/dubbo/remoting/transport/netty/NettyServer.java	67.85% <0%> (-3.58%)	8% <0%> (-1%)
.../dubbo/rpc/protocol/dubbo/filter/FutureFilter.java	54.54% <0%> (-2.03%)	13% <0%> (ø)
.../com/alibaba/dubbo/monitor/dubbo/DubboMonitor.java	87.85% <0%> (-1.87%)	15% <0%> (ø)
...dubbo/rpc/protocol/dubbo/CallbackServiceCodec.java	77.2% <0%> (-1.48%)	29% <0%> (ø)
...libaba/dubbo/rpc/protocol/dubbo/DubboProtocol.java	60.08% <0%> (-0.88%)	32% <0%> (-1%)
.../java/com/alibaba/dubbo/common/json/JSONArray.java
... and 10 more

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