fix leaked exception in RRuleLocator.tick_values

[gnaggnoyil]

The tick_values method of RRuleLocator in matlotlib.dates module uses dateutil module to calculate the datetime padding in an axis and in case the padding go out of leftist bound it will be set to num2date(1.0). However, in the case when the calculation of datetime goes out of bound, not only the ValueError will be thrown, but also OverflowError will. Not catching OverflowError would cause this exception to propagate through the call stack and ultimately prevent the main program from executing. This patch is intended to fix the bug, and a case that would cause this bug is added in test_dates.py in test_RRuleLocator_dayrange function.

[tacaswell]

You do not need the try...except here. If it raises, then the test will fail (but the exception will be caught and the rest of the test suite will run).

Just a comment about how this is just testing 'does not raise' is enough.

[tacaswell]

Thank you for your work on this!

The test failure is a style violation (just some trailing whitespace).

=================================== FAILURES ===================================
 PEP8-check(ignoring E111 E114 E115 E116 E121 E122 E123 E124 E125 E126 E127 E128 E129 E131 E226 E240 E241 E242 E243 E244 E245 E246 E247 E248 E249 E265 E266 E704 W503) 
[gw1] linux -- Python 3.6.2 /home/travis/build/matplotlib/matplotlib/venv/bin/python
/home/travis/build/matplotlib/matplotlib/lib/matplotlib/tests/test_dates.py:144:1: W293 blank line contains whitespace
^

I left a comment on the test, it can be simplified a bit.

In general 👍 .

If you have any questions please ask!

[gnaggnoyil]

@tacaswell Thanks for your reviewing! I've updated the pull request as requested. Does the travis-ci job for this project check every snapshot for a pull request, or only check for the latest one?

[tacaswell]

Thanks @gnaggnoyil ! I think this was your first Matplotlib PR, congratulations 🎉 Hopefully we will hear from you again!

To answer your question about travis, it triggers on every push to the PR branch an runs on the merge of the tip of the branch into the current master branch.