Allow missing `ishape_last.txt` in `comp_ishape`

Allow missing `ishape_last.txt` in method `comp_ishape`. This is
useful is an SHPC is missing an orientation.

Common/util_eddies.py

@@ -177,8 +177,11 @@ class SHPC_class:
             ishape = eddy_index - 1
         else:
             # date > self.d_init[i_slice]
-            ishape = self.get_ishape_last(i_slice, orientation)\
-                [date - self.d_init[i_slice] - 1] + eddy_index
+            try:
+                ishape = self.get_ishape_last(i_slice, orientation)\
+                    [date - self.d_init[i_slice] - 1] + eddy_index
+            except TypeError:
+                ishape = None
 
         return ishape