SEN2COR and missing SRTM-files from CGIAR (tiles over water)

In some cases SEN2COR tries to download SRTM tiles from CGIAR website even these don’t exist. SEN2COR does not handle this situation gracefully and that leads to some errors during processing.
Example: For the product S2A_OPER_PRD_MSIL1C_PDMC_20160620T185521_R049_V20160620T075548_20160620T075548.SAFE SEN2COR tries to download the non-existing tile 44/18 (water), creates a empty zip file in the dem directory and cannot unzip this file. Actually SEN2COR should ignore the DEM and use flat data.

The bug is within the

This is the only case where SEN2COR uses flat data (tiles outside the CGIAR tile system):