ArwDecoder::decodeRawInternal(): safer check for arw1.
ArwDecoder::decodeRawInternal(): safer check for arw1.

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