calc_hairpin() `structure_found == True` even no hairpin structure?

[dodoflyy]

Hey, it seems sometimes calc_hairpin() will output structure_found=True but the running message is "No secondary structure could be calculated". Example:

>>> from primer3 import thermoanalysis
>>> thermo_analysis = thermoanalysis.ThermoAnalysis()
>>> thermo_analysis.calc_hairpin("GAAAGGGATGGGGGACTTGG", output_structure=True)
No secondary structure could be calculated
ThermoResult(structure_found=True, tm=0.00, dg=0.00, dh=0.00, ds=0.00)

And the rest attributes are zero, strange?

Edit: I think the problem is structure_found always returns true.

[grinner]

fix merged into 2.0.0-staging branch