FileMap: offset==size is not valid
FileMap: offset==size is not valid

When offset==size we're exactly 1byte over the end of the
file so reject that location.

klauspost/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,anarsoul/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,klauspost/rawspeed,anarsoul/rawspeed,anarsoul/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed