BF: pass original exception into replace_surrogate_encode

[yarikoptic]

Fixes my incorrect fix in #598 ;-)

[codecov-io]

Codecov Report

Merging #603 into master will increase coverage by 0.02%.
The diff coverage is 33.33%.

@@ Coverage Diff @@## master #603 +/- ##
=========================================
+ Coverage 94.48% 94.5% +0.02% 
=========================================
Files 63 63 Lines 9961 9961 =========================================
+ Hits 9412 9414 +2 + Misses 549 547 -2

Impacted Files	Coverage Δ
git/compat.py	63.19% <33.33%> (ø)	✅
git/test/test_repo.py	97.47% <0%> (+0.33%)	✅

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[Byron]

That's how it was meant to be! Thanks for figuring it out!