Tweak JmsMessagingTemplateTests for Eclipse 4.4

Eclipse 4.4 early release versions have issues with generics.

This commit slightly tweaks the use of generics in
JmsMessagingTemplateTests so that the class compiles in the latest
builds of Eclipse 4.4
Throw a proper exception if no convert is found

Prior to this commit, no exception was raised if a message could not
be converted to the requested payload because no suitable converter
were found.

This commit adds an explicit check if the converted payload is null.

Issue: SPR-11817
SPR-11825 SubPWSocketH: eventPublisher population

JIRA: https://jira.spring.io/browse/SPR-11825

As long as `StompSubProtocolHandler` has been created directly in case of `@EnableWebSocketMessageBroker`,
there was no application context infrastructure population.

Make `WebMvcStompEndpointRegistry` as `ApplicationContextAware` and populate it to the
`StompSubProtocolHandler.setApplicationEventPublisher`

**Cherry-pick to 4.0.x**