Fix occasional "table already defined" in JobsView

[my8100]

No description provided.

[pep8speaks]

Hello @my8100! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file scrapydweb/utils/check_app_config.py:

Line 111:80: E501 line too long (102 > 79 characters)

• In the file scrapydweb/views/overview/jobs.py:

Line 171:80: E501 line too long (95 > 79 characters)
Line 303:80: E501 line too long (86 > 79 characters)
Line 308:80: E501 line too long (109 > 79 characters)
Line 348:80: E501 line too long (104 > 79 characters)

[codecov]

Codecov Report

Merging #68 into master will decrease coverage by 0.25%.
The diff coverage is 88.23%.

@@            Coverage Diff             @@
##           master      #68      +/-   ##
==========================================
- Coverage    89.5%   89.24%   -0.26%     
==========================================
  Files          30       30              
  Lines        3543     3552       +9     
==========================================
- Hits         3171     3170       -1     
- Misses        372      382      +10

Impacted Files	Coverage Δ
scrapydweb/views/overview/tasks.py	98.1% <ø> (ø)	⬆️
scrapydweb/vars.py	98.07% <100%> (+0.03%)	⬆️
scrapydweb/utils/check_app_config.py	84.93% <100%> (+0.32%)	⬆️
scrapydweb/views/overview/jobs.py	92.23% <80%> (-1.89%)	⬇️
scrapydweb/common.py	84.12% <0%> (-6.35%)	⬇️

[coveralls]

Pull Request Test Coverage Report for Build 72

• 15 of 17 (88.24%) changed or added relevant lines in 3 files are covered.
• 6 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.08%) to 88.795%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
scrapydweb/views/overview/jobs.py	8	10	80.0%

Files with Coverage Reduction	New Missed Lines	%
scrapydweb/views/overview/jobs.py	6	91.59%

Totals
Change from base Build 55:	-0.08%
Covered Lines:	3154
Relevant Lines:	3552

---

💛 - Coveralls