Fix #430: blank inputs for DOSXYZnrc sources
Fix #430: blank inputs for DOSXYZnrc sources

Fix a bug in inputs for sources 20 and 21 in which the code hung if the
user indicated that a shared library geometry was not to be included by
inputting a blank (instead of a '0') for the name of code defining the
shared library geometry.

While fixing this, other input bugs related to incorrect use of the
Fortran len(char) were found and fixed.

mchamberland/EGSnrc,marenaud/EGSnrc,mchamberland/EGSnrc,nrc-cnrc/EGSnrc,marenaud/EGSnrc,ftessier/EGSnrc,MartinMartinov/EGSnrc,nrc-cnrc/EGSnrc,marenaud/EGSnrc,marenaud/EGSnrc,MartinMartinov/EGSnrc,mchamberland/EGSnrc,MartinMartinov/EGSnrc,MartinMartinov/EGSnrc,crcrewso/EGSnrc,crcrewso/EGSnrc,ftessier/EGSnrc,crcrewso/EGSnrc,nrc-cnrc/EGSnrc,marenaud/EGSnrc,crcrewso/EGSnrc,mchamberland/EGSnrc,nrc-cnrc/EGSnrc,crcrewso/EGSnrc,mchamberland/EGSnrc,ftessier/EGSnrc,MartinMartinov/EGSnrc,nrc-cnrc/EGSnrc,ftessier/EGSnrc,mchamberland/EGSnrc,ftessier/EGSnrc,ftessier/EGSnrc,marenaud/EGSnrc