Fixes deadlock when closing an input channel to a component with multiple input channels

[seanward]

Sample code to produce deadlock included (examples/multi-input.go). Did not test the implications on pool mode or your new looper components however. Root issue is a need for one port handler to be executing (or executed) per input channel.

[trustmaster]

@seanward thanks! Could you please provide a simple test case with just one component in component_test.go instead of the example so we can be sure there won't be regressions in future?

[pgruenbacher]

@seanward thanks Sean!

[trustmaster]

Closing as outdated