Fix a debug print in disassembler (#14905)

Authored by osa1 on Mar 9 2018, 6:38 AM.

Description

Fix a debug print in disassembler (Trac #14905)

When interpreter is not profiled (see interpreterProfiled in
DynFlags) bytecode generator generates a NULL pointer as the cost
centre of a BRK_FUN instruction:

let cc | interpreterProfiled dflags = cc_arr ! tick_no
       | otherwise = toRemotePtr nullPtr
let breakInstr = BRK_FUN (fromIntegral tick_no) (getUnique this_mod) cc
return $ breakInstr `consOL` code

We now take this into account when disassembling BRK_FUN.

Reviewers: bgamari, simonmar, erikd

Subscribers: rwbarton, thomie, carter

Differential Revision: https://phabricator.haskell.org/D4490