fix(debugging): Do not close data socket prematurely

[mbektchiev]

Multiple dispatch_io operations are usually running simultaneously. When recreating the inspector listening socket after an "AttachRequest" notification from {N} CLI, the following crash happened in a dispather worker thread: BUG IN CLIENT OF LIBDISPATCH: Unexpected EV_VANISHED (do not destroy random mach ports or file descriptors)

The reason turned out to be that we always have at least 2 pending current operations. One is reading the next message, and the other one -- the cleanup handler from dispatch_io_create.

PR Checklist

• [x] The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• [x] There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• [x] You have signed the CLA.
• [x] All existing tests are passing: https://github.com/NativeScript/ios-runtime/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• [ ] Tests for the changes are included.

refs #1254