fix(SSEHandlerImp): shouldn't reject connection when no Accept header

[ctranxuan]

Hello, When a client tries to connect to the SSEHandler with no Accept header (eg via a curl), the connection is rejected with a 406. The spec (https://www.w3.org/TR/2015/REC-eventsource-20150203/#text-event-stream) says however:

For HTTP connections, the Accept header may be included; if included, it must contain only formats of event framing that are supported by the user agent (one of which must be text/event-stream, as described below).

So, in case there is no Accept header, the connection shouldn't be rejected.

The fix changes the condition of the SSEHandlerImpl to only reject connections when there is Accept headers that don't include "text/event-stream". If there is no Accept header, there is no rejection.

Note: the latest spec (https://html.spec.whatwg.org/multipage/server-sent-events.html#server-sent-events) doesn't mention this anymore.

[codecov-io]

Codecov Report

Merging #12 into master will increase coverage by 0.54%. The diff coverage is 100%.

@@             Coverage Diff              @@
##             master      #12      +/-   ##
============================================
+ Coverage     89.18%   89.72%   +0.54%     
- Complexity       69       70       +1     
============================================
  Files            10       10              
  Lines           185      185              
  Branches         20       20              
============================================
+ Hits            165      166       +1     
  Misses           11       11              
+ Partials          9        8       -1

Impacted Files	Coverage Δ	Complexity Δ
...vertx/ext/web/handler/sse/impl/SSEHandlerImpl.java	100% <100%> (+3.44%)	9 <0> (+1)	:arrow_up:

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[aesteve]

Thanks a lot !