`mark_cis_trans()` warns "cannot represent cis/trans bond between atoms" even for structures without cis/trans bonds

[merkys]

A warning statement is executed too eagerly in mark_cis_trans(), even for structures having no cis/trans bonds. Observed in v0.10.0 with the following SMILES from the COD:

c1(cc(ccc1N=N[C@@H](C)CC[C@H]1[C@]2(C[C@@H](C[C@]1(C)OC2)OC(=O)c1ccc(cc1)N(=O)=O)C)N(=O)=O)N(=O)=O.c1(cc(ccc1N=N[C@H](C)CC[C@@H]1[C@@]2(C[C@H](C[C@@]1(C)CO2)OC(=O)c1ccc(cc1)N(=O)=O)C)N(=O)=O)N(=O)=O	1504511

[merkys]

This has been addressed in v0.11.0, at least to some extent.