Report fails to generate when some test don't use RobotEyes feature

[kumy]

Describe the bug
Only few of my tests use RobotEyes. The reportgen fails to generate the report with error:

13 tests total, 13 passed, 0 failed
==============================================================================
Debug:   /home/kumy/GIT/geokrety-website_new-theme/tests-qa/docs/local/debugfile.log
Output:  /home/kumy/GIT/geokrety-website_new-theme/tests-qa/docs/local/output.xml
XUnit:   /home/kumy/GIT/geokrety-website_new-theme/tests-qa/docs/local/xUnit.xml
Log:     /home/kumy/GIT/geokrety-website_new-theme/tests-qa/docs/local/log.html
Report:  /home/kumy/GIT/geokrety-website_new-theme/tests-qa/docs/local/report.html
Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python3.8/threading.py", line 932, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.8/threading.py", line 870, in run
    self._target(*self._args, **self._kwargs)
  File "/home/kumy/GIT/geokrety-website-qa/venv/lib/python3.8/site-packages/RobotEyes/report_generator.py", line 60, in generate_report
    for filename in os.listdir(baseline_folder + os.path.sep + folder_name):
FileNotFoundError: [Errno 2] No such file or directory: 'visual_images/Seed'

To Reproduce
Steps to reproduce the behavior:

1. Have Test Cases with and without RobotEyes
   ex:

Library         SeleniumLibrary  timeout=10  implicit_wait=0
Library         RobotEyes

*** Test Cases ***

Seed
    Seed 1 users
    
Statpic generated on user create
    Seed 1 users
    Go To User 1 url
    Check Image

Statpic updated on geokrety create
    Seed 1 users
    Seed 1 geokrety owned by 1
    Go To User 1 url
    Check Image

*** Keywords ***
Check Image
    Open Eyes    SeleniumLibrary  5
    Wait Until Element Is Visible           ${USER_PROFILE_STATPIC_IMAGE}
    Capture Element                         ${USER_PROFILE_STATPIC_IMAGE}
    Compare Images

2. Start Robot Framework
3. See error when report is generated

Expected behavior
No error should happen when some tests don't use Open Eyes keyword

Screenshots
N/A

Desktop (please complete the following information):

$ python --version
Python 3.8.2

$ pip freeze|grep eye
robotframework-eyes==1.4.1

[kumy]

Please find PR #65

[jessezach]

Merged the fix. Will go out in release 1.5.0