Handle ValueError in mashmallow validation

Part of: #859

Author: stefanor

hug/types.py

@@ -727,6 +727,8 @@ def __call__(self, value):
                 value = self.schema.dump(value)
             except ValidationError as e:
                 errors = e.messages
+            except ValueError as e:
+                errors = [str(e)]
 
         if errors:
             raise InvalidTypeData(