[thermo] Throw IndexError for invalid species index

[ischoegl]

Changes proposed in this pull request

• raise IndexError for invalid species
• use existing checkSpeciesIndex method

In [1]: import cantera as ct
   ...: gas = ct.Solution('gri30.yaml')
   ...: 

In [2]: gas.species(53)
---------------------------------------------------------------------------
CanteraError                              Traceback (most recent call last)
<ipython-input-2-1d8e247355bb> in <module>()
----> 1 gas.species(53)

/src/interfaces/cython/cantera/thermo.pyx in cantera._cantera.ThermoPhase.species()
    592             s._assign(self.thermo.species(stringify(k)))
    593         elif isinstance(k, (int, float)):
--> 594             s._assign(self.thermo.species(<int>k))
    595         else:
    596             raise TypeError("Argument must be a string or a number."

CanteraError: 
***********************************************************************
IndexError thrown by Phase::checkSpeciesIndex:
IndexError: species[53] outside valid range of 0 to 52.
***********************************************************************

If applicable, fill in the issue number this pull request is fixing

Fixes #948

Checklist

• There is a clear use-case for this code change
• The commit message has a short title & references relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• The pull request is ready for review

[codecov]

Codecov Report

Merging #949 (fe7789f) into main (d8e62ad) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #949   +/-   ##
=======================================
  Coverage   71.22%   71.22%           
=======================================
  Files         377      377           
  Lines       46272    46273    +1     
=======================================
+ Hits        32955    32957    +2     
+ Misses      13317    13316    -1     

Impacted Files	Coverage Δ
src/thermo/Phase.cpp	82.84% <100.00%> (+0.21%)	⬆️

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[speth]

Seems simple enough to me.