Bad error if dynamic or hybrid library returns invalid keyword names

[pekkaklarck]

If a dynamic or hybrid library returns invalid keyword names (i.e. doesn't return a list of Unicode or UTF-8 strings), the resulting error doesn't contain the name of the invalid library.

This problem can be reproduced with the following library and test data. Running them causes an error like Error in file '/path/inv_dyn.robot': Calling dynamic method 'get_keyword_names' failed: Return value must be list of strings.. Same problem may also occur with other dynamic methods.

class Invalid(object):
    def get_keyword_names(self):
        return 1

*** Settings ***
Library  Invalid.py

*** Test Cases ***
Example
    Log    whatever