FIx a crash from invalid iterator

:Release Notes:
Fixed an occasional crash in nodejs

:Detailed Notes:
The nodejs-module-webos-sysbus add-on was manipulating a C++ iterator in a bad way. Fixed
the code so it no longer crashes.

:Testing Performed:
CHecked that iterator is no longer manipulated after being invalidated.

:QA Notes:

:Issues Addressed:
[GF-25567] nodejs crash due to pollwMap iterator invalidation

Open-webOS-DCO-1.0-Signed-off-by: Mark Bessey <mark.bessey@lge.com>

Change-Id: I5aa598f52ccefdc0a215dae1e7784fae3218f2bd
Reviewed-on: https://g2g.palm.com/3154
Reviewed-by: Build Verification
Reviewed-by: Vinay Ramachandra <ramachandra.vinay@lge.com>
Reviewed-by: Jason Lai <jason.lai@lge.com>
Reviewed-by: Mark Bessey <mark.bessey@lge.com>
Tested-by: Mark Bessey <mark.bessey@lge.com>