Fix PGPOINT scalar/array mismatch in best.f and quickplot.f

[alex88ridolfi]

Trying to compile sigproc on Ubuntu 24.04 with gfortran GNU Fortran 13.3.0 (Ubuntu 13.3.0-6ubuntu2~24.04.1), I was encountering errors such as:

f77 -fno-second-underscore -g -O2 -c -o best.o best.f
best.f:791:33:

  788 |                   call pgpoint(ndm,x,y,17)
      |                                   2
......
  791 |                   call pgpoint(1,xx,yy,27)
      |                                 1
Error: Rank mismatch between actual argument at (1) and actual argument at (2) (rank-1 and scalar)
best.f:791:36:

  788 |                   call pgpoint(ndm,x,y,17)
      |                                     2
......
  791 |                   call pgpoint(1,xx,yy,27)
      |                                    1
Error: Rank mismatch between actual argument at (1) and actual argument at (2) (rank-1 and scalar)
make[3]: *** [Makefile:1689: best.o] Error 1
make[3]: Leaving directory '/home/ridolfi/SOFT/sigproc/src'
make[2]: *** [Makefile:1037: all] Error 2
make[2]: Leaving directory '/home/ridolfi/SOFT/sigproc/src'
make[1]: *** [Makefile:452: all-recursive] Error 1
make[1]: Leaving directory '/home/ridolfi/SOFT/sigproc'
make: *** [Makefile:384: all] Error 2

With the help of Copilot, I introduced the necessary fixes to best.f and quickplot.f for compilation to be successful.