Fix error parsing latex_symbols.js from Julia.

[accidentalrebel]

This fix makes sure that the code checks if whether each parsed line has a " character. Otherwise it skips it.

This is the first step to allow iPython to parse and update it's latex symbols. Related to ipython#12861.

Before this fix, an error occurs when gen_latex_symbols.py is called.

$ python3 gen_latex_symbols.py 
Importing latex_symbols.js from Julia...
Building a list of (latex, unicode) key-value pairs...
Traceback (most recent call last):
  File "/home/arebel/development/open-source/ipython/tools/gen_latex_symbols.py", line 42, in <module>
    x, y = x.split('"')[1], y.split('"')[1] # get the values in quotes
IndexError: list index out of range

This is caused by line 2629 of: https://github.com/raw/JuliaLang/julia/master/stdlib/REPL/src/latex_symbols.jl.