Fix #664 fixing param s in AB-join mode

[NimaSarajpoor]

This PR resolves the issue raised in #664. When s=None and T_B is not None, the value of s remains None in scrump and prescrump and their non-normalized versions. I used the suggestion provided by @seanlaw (in #664) to fix the issue.

[codecov-commenter]

Codecov Report

Merging #665 (3700791) into main (d1469aa) will decrease coverage by 0.01%.
The diff coverage is 66.66%.

@@ Coverage Diff @@## main #665 +/- ##
==========================================
- Coverage 99.89% 99.87% -0.02% 
==========================================
Files 80 80 Lines 11451 11455 +4 ==========================================
+ Hits 11439 11441 +2 - Misses 12 14 +2 

Impacted Files	Coverage Δ
stumpy/scraamp.py	99.29% <66.66%> (-0.71%)	⬇️
stumpy/scrump.py	99.31% <66.66%> (-0.69%)	⬇️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[NimaSarajpoor]

I think we got the imprecision issue again, caused by identical sequence (see PR #657)

[seanlaw]

Thanks for addressing this @NimaSarajpoor!