fix(project config manager): Don't log an error when not initialized with datafile

[mjc1283]

Summary

Fixes a regression introduced during refactoring for datafile accessor - any time the datafile property of the object passed to createInstance is missing or falsy, the logger will output (for example):

[OPTIMIZELY] - ERROR 2020-10-05T23:38:15.224Z CONFIG_VALIDATOR: No datafile specified. Cannot start optimizely

Passing in an sdkKey, but no datafile, is valid and supported when calling createInstance, but this message leads the user to believe otherwise. In this situation, nothing is actually wrong, but the message says "Cannot start optimizely".

To fix, in ProjectConfigManager __initialize, when config.datafile is falsy, we do not call __handleNewDatafile, avoiding the code path that eventually would log the error message.

Test plan

• Added new unit test
• Manually tested

[coveralls]

Coverage increased (+0.003%) to 96.631% when pulling 8ffd5d9 on mcarroll/fix-error-when-not-initialized-with-datafile into f75c4fb on master.

[aliabbasrizvi]

LGTM