[BUGFIX] Prevent NPE on WS decode without SSL config

[damiantw]

Prevents an NPE when decoding a WebSocket request while ssl.ssl_server_cert_path and ssl.ssl_server_key_path is not configured.

rsc-server  |      [java] io.netty.handler.codec.DecoderException: java.lang.NullPointerException: sslContext
rsc-server  |      [java]       at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:472) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:278) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1408) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:930) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:163) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:677) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:612) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:529) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:491) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:905) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at com.openrsc.server.util.ServerAwareThreadFactory.lambda$newThread$0(ServerAwareThreadFactory.java:20) ~[core.jar:?]
rsc-server  |      [java]       at java.lang.Thread.run(Thread.java:833) [?:?]
rsc-server  |      [java] Caused by: java.lang.NullPointerException: sslContext
rsc-server  |      [java]       at io.netty.util.internal.ObjectUtil.checkNotNull(ObjectUtil.java:33) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.handler.ssl.OptionalSslHandler.<init>(OptionalSslHandler.java:39) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at com.openrsc.server.net.RSCMultiPortDecoder.addWebHandlerStack(RSCMultiPortDecoder.java:55) ~[core.jar:?]
rsc-server  |      [java]       at com.openrsc.server.net.RSCMultiPortDecoder.decode(RSCMultiPortDecoder.java:36) ~[core.jar:?]
rsc-server  |      [java]       at io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:502) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:441) ~[netty-all-4.1.33.Final.jar:4.1.33.Final]
rsc-server  |      [java]       ... 16 more