Graceful exit for gris_lot_cont_corr

Plot cont corr should exit with a warning if no files are found:

Wed Mar 16 01:43:35 CET 2022
running gris_plot_cont_corr --store /dat/sdc/gris/20191003/context_data/*cont_corr*sav

 __  ___  __       _______.   .___________.  ______     ______    __          _______.
|  |/  / |  |     /       |   |           | /  __  \   /  __  \  |  |        /       |
|  '  /  |  |    |   (----`   `---|  |----`|  |  |  | |  |  |  | |  |       |   (----`
|    <   |  |     \   \           |  |     |  |  |  | |  |  |  | |  |        \   \    
|  .  \  |  | .----)   |          |  |     |  `--'  | |  `--'  | |  `----.----)   |   
|__|\__\ |__| |_______/           |__|      \______/   \______/  |_______|_______/    

Traceback (most recent call last):
  File "/home/schaffer/anaconda3/envs/sdc/bin/gris_plot_cont_corr", line 7, in <module>
    exec(compile(f.read(), __file__, 'exec'))
  File "/dat/schaffer/projects/kis_tools/bin/gris_plot_cont_corr", line 27, in <module>
    fig = plot_cont_corr(i)
  File "/dat/schaffer/projects/kis_tools/kis_tools/gris/plotting.py", line 140, in plot_cont_corr
    data = readsav(path)
  File "/home/schaffer/anaconda3/envs/sdc/lib/python3.10/site-packages/scipy/io/idl.py", line 738, in readsav
    f = open(file_name, 'rb')
FileNotFoundError: [Errno 2] No such file or directory: '/dat/sdc/gris/20191003/context_data/*cont_corr*sav'
/var/lib/condor/execute/dir_326475/condor_exec.exe: line 105: [: ==: unary operator expected