SSA conversion drops bool typecheck for noop if

[Keno]

Actual:

julia> f() = (if nothing; end; unsafe_load(Ptr{Int}(0)))
f (generic function with 1 method)

julia> f()
Unreachable reached at 0x7fb33bb50090

signal (4): Illegal instruction
in expression starting at REPL[13]:1
unsafe_load at ./pointer.jl:105 [inlined]
unsafe_load at ./pointer.jl:105 [inlined]

Expected:

ERROR: TypeError: non-boolean (Nothing) used in boolean context
Stacktrace:
 [1] f()
   @ Main ./REPL[1]:1
 [2] top-level scope
   @ REPL[2]:1