VC5Decompressor::Wavelet::reconstructLowband(): be more specific about memory live-range
VC5Decompressor::Wavelet::reconstructLowband(): be more specific about memory live-range

We only need for those 3 tmp buffers to exist until we compute
the lowpass and highpass, we don't need them afterwarsds.

We *could* also delay creation of the final 'dest'.

darktable-org/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed