Fix 85: Fix NaN pegs4 data when compiled with -ffast-math
Fix 85: Fix NaN pegs4 data when compiled with -ffast-math

Error traced to variable VPLASM=SQRT(EDEN*R0*C^2/PI)=Infinity with
certain inputs when -ffast-math compiler option used.  Order of
operations changed to ensure argument inside SQRT() not infinite.
Thus, VPLASM=SQRT(EDEN/PI*R0*C^2).
mchamberland/EGSnrc,ftessier/EGSnrc,ftessier/EGSnrc,marenaud/EGSnrc,mchamberland/EGSnrc,mchamberland/EGSnrc,mchamberland/EGSnrc,crcrewso/EGSnrc,marenaud/EGSnrc,crcrewso/EGSnrc,marenaud/EGSnrc,ftessier/EGSnrc,mchamberland/EGSnrc,ftessier/EGSnrc,marenaud/EGSnrc,nrc-cnrc/EGSnrc,marenaud/EGSnrc,ftessier/EGSnrc,MartinMartinov/EGSnrc,crcrewso/EGSnrc,MartinMartinov/EGSnrc,ftessier/EGSnrc,marenaud/EGSnrc,nrc-cnrc/EGSnrc,mchamberland/EGSnrc,nrc-cnrc/EGSnrc,MartinMartinov/EGSnrc,nrc-cnrc/EGSnrc,crcrewso/EGSnrc,crcrewso/EGSnrc,nrc-cnrc/EGSnrc,MartinMartinov/EGSnrc,MartinMartinov/EGSnrc