no similarity on ssdeeps from similar files

[CaldurG]

Pls see files in this archive
They are quite similar, but ssdeep returns 0 similarity on 2 of them. This is caused by has_common_substring(_pa) check in score_strings function. Without it I get score 60. Btw there is negligible performance impact if you remove it.

0.txt ssdeep: 24:+RPhWeV1T3rQ+QV1T3rQXV1T3rQ62H2M3kpann:uPAefDM+QfDMXfDM62H2Mkp6
1.txt ssdeep: 24:+RPy6qV1T3rQcV1T3rQ64V1T3rQqV1T3rQ0pa5:uPUfDMcfDM64fDMqfDM0pe
2.txt ssdeep: 24:+RP4zpirdqV1T3rQxunV1T3rQ8V1T3rQxV1T3rQTpa5:uP4zgr4fDMYnfDM8fDMxfDMTpe
0.txt vs 1.txt: 65
0.txt vs 2.txt: 0
1.txt vs 2.txt: 77