IODI - Fix edge case where debug item exists but code_item has no instructions
IODI - Fix edge case where debug item exists but code_item has no instructions

Summary:
Paired with danzimm to fix this one.

While running IODI on production APK [197718206](https://our.intern.facebook.com/intern/mobile/buildinfo/buildinfo/?build=197718206) we found that the program would fail when a code item has no instructions but does have a debug item.

We don't need to emit debug information for empty methods anyways, so this diff adds code to skip that.

Reviewed By: danzimm

Differential Revision: D19835397

fbshipit-source-id: 2bfff418a907af3cb97214a188114de77af3b9d3

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex