[API] Return http error if requested code cannot be compiled

[wwerner]

Currently, when requesting code for a specification that cannot be parsed,
the request hangs w/ sth. like the exception below.

We should return an HTTP error response in this case.

12:08:07.622 [pool-2-thread-4] DEBUG io.vlingo.actors.Logger - COMPILING:     khlkjljlk
line 1:4 mismatched input 'khlkjljlk' expecting {'command', 'data', 'document', 'envelope', 'event', 'metadata'}
12:08:07.656 [pool-2-thread-6] ERROR io.vlingo.actors.Logger - Message#deliver(): Exception: null for Actor: Actor[type=AntlrTypeParser address=GridAddress[id=6834f14a-f3a2-4c24-83da-b86420060825, name=(none)]] sending: parseTypeDefinition(java.io.InputStream, java.lang.String)
java.lang.NullPointerException: null
	at io.vlingo.schemata.codegen.parser.AntlrTypeParser.parseTypeDeclaration(AntlrTypeParser.java:68) ~[classes/:na]
	at io.vlingo.schemata.codegen.parser.AntlrTypeParser.parseTypeDefinition(AntlrTypeParser.java:51) ~[classes/:na]
	at io.vlingo.schemata.codegen.parser.TypeParser__Proxy.lambda$parseTypeDefinition$0(TypeParser__Proxy.java:29) ~[classes/:na]
	at io.vlingo.actors.LocalMessage.internalDeliver(LocalMessage.java:115) ~[classes/:na]
	at io.vlingo.actors.LocalMessage.deliver(LocalMessage.java:47) ~[classes/:na]
	at io.vlingo.actors.plugin.mailbox.concurrentqueue.ConcurrentQueueMailbox.run(ConcurrentQueueMailbox.java:101) ~[classes/:na]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) ~[na:1.8.0_212]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) ~[na:1.8.0_212]
	at java.lang.Thread.run(Thread.java:748) ~[na:1.8.0_212]
12:08:07.656 [pool-2-thread-6] ERROR io.vlingo.actors.Logger - DefaultSupervisorOverride: Failure of: GridAddress[id=6834f14a-f3a2-4c24-83da-b86420060825, name=(none)] because: null Action: Resuming.
java.lang.NullPointerException: null
	at io.vlingo.schemata.codegen.parser.AntlrTypeParser.parseTypeDeclaration(AntlrTypeParser.java:68) ~[classes/:na]
	at io.vlingo.schemata.codegen.parser.AntlrTypeParser.parseTypeDefinition(AntlrTypeParser.java:51) ~[classes/:na]
	at io.vlingo.schemata.codegen.parser.TypeParser__Proxy.lambda$parseTypeDefinition$0(TypeParser__Proxy.java:29) ~[classes/:na]
	at io.vlingo.actors.LocalMessage.internalDeliver(LocalMessage.java:115) ~[classes/:na]
	at io.vlingo.actors.LocalMessage.deliver(LocalMessage.java:47) ~[classes/:na]
	at io.vlingo.actors.plugin.mailbox.concurrentqueue.ConcurrentQueueMailbox.run(ConcurrentQueueMailbox.java:101) ~[classes/:na]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) ~[na:1.8.0_212]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) ~[na:1.8.0_212]
	at java.lang.Thread.run(Thread.java:748) ~[na:1.8.0_212]