lmul!(0, A) should replace NaN with 0.0

[dlfivefifty]

Standard arrays have the feature that lmul!(0.0, A) replaces NaNs with 0.0, consistent with BLAS:

julia> lmul!(0.0,fill(NaN,3,3))
3×3 Array{Float64,2}:
 0.0  0.0  0.0
 0.0  0.0  0.0
 0.0  0.0  0.0

This is gone when generic_lmul! is called:

julia> lmul!(0,fill(NaN,3,3))
3×3 Array{Float64,2}:
 NaN  NaN  NaN
 NaN  NaN  NaN
 NaN  NaN  NaN

I'd propose fixing this inconsistency by making generic_lmul! follow the BLAS convention.

[raghav9-97]

I tried to reproduce the problem and got following results
julia> lmul!(0.0,fill(NaN,3,3))

 NaN  NaN  NaN
 NaN  NaN  NaN
 NaN  NaN  NaN

Julia Version 1.1.0-DEV.823
Commit c3b2bbb (2018-12-06 10:55 UTC)
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-6.0.1 (ORCJIT, skylake)

[dlfivefifty]

Julia 1.1-pre has actually gone the other way and changed the behaviour for BLAS types. I think this issue can therefore be closed?