Fix resubmit_unconverged_geometry handler. (#116)

Currently, an AiiDA Dict object defined as follows:
```
d = Dict(dict={'a':{'b':1}})
```
Returns two type of errors if the key isn't present:
- `d['x']` returns `AttributeError`
- `d['a']['x'] returns `KeyError`

This PR adapts the `resubmit_unconverged_geometry` handler to
this behaviour.

aiida_cp2k/workchains/base.py

@@ -74,7 +74,7 @@ def resubmit_unconverged_geometry(self, calc):
                     params = add_restart_sections(params)
 
             # If not all the restart keys are present, adding them to the input dictionary
-            except KeyError:
+            except (AttributeError, KeyError):
                 params = add_restart_sections(params)
 
             # Might be able to solve the problem