graceful ending when no coord file is found

[tobigithub]

Hi,
this is for version 5.1.0, when no coord file is found, QCxMS should tell the user what to do, instead of a hard crash.
Something like, "No coord inputfile found, please provide input coordinates. "
Tobias

              ************************************************************
                       Mode:          Electron Impact (EI)
              ************************************************************
forrtl: No such file or directory
forrtl: severe (29): file not found, unit -130, file /qcxms-runs/coord
Image              PC                Routine            Line        Source
qcxms              0000000002A66B58  Unknown               Unknown  Unknown
qcxms              0000000002A82B62  Unknown               Unknown  Unknown
qcxms              00000000004837BC  read_coordinates_          54  rdcoord.f90
qcxms              0000000000401E5E  MAIN__                    318  main.f90
qcxms              0000000000400DF2  Unknown               Unknown  Unknown
qcxms              0000000002C92529  Unknown               Unknown  Unknown
qcxms              0000000000400CCA  Unknown               Unknown  Unknown

[JayTheDog]

Fixed and added.