Move input of `N_eddies` and `date_num` higher

Before input of `id_child` because reading `N_eddies` and `date_num` is
very quick, while reading `id_child` is long. So we do not waste time
if `N_eddies.mat` or `date_num.mat` are missing.

Convert_Matlab/overlap_v6.py

@@ -29,6 +29,9 @@ def adjust_n(n_Matlab):
 if __name__ == "__main__":
     n_files = input("Number of input files id_child_*.mat? ")
     n_files = int(n_files)
+    n_eddies = sio.loadmat("N_eddies.mat", squeeze_me = True)["N_eddies"]\
+                  .astype(int, casting = "safe", copy = False)
+    date_num = sio.loadmat("date_num.mat", squeeze_me = True)["date_num"]
     id_child_list = []
 
     for i in range(n_files):
@@ -47,9 +50,6 @@ if __name__ == "__main__":
     else:
         id_child = part_id_child
 
-    n_eddies = sio.loadmat("N_eddies.mat", squeeze_me = True)["N_eddies"]\
-                  .astype(int, casting = "safe", copy = False)
-    date_num = sio.loadmat("date_num.mat", squeeze_me = True)["date_num"]
     n_dates = n_eddies.size
     print("n_dates =", n_dates)
     e_overestim = id_child.shape[0]