NODATA reader in geotiff reader rebuilt so it reads the value similar as the GDAL source code.

This PR reads the value as the GDAL source code does.

Check these links for exactly how:

https://github.com/OSGeo/gdal/blob/trunk/gdal/frmts/gtiff/geotiff.cpp#L6686
 https://github.com/OSGeo/gdal/blob/trunk/gdal/port/cpl_strtod.cpp#L143