encoding/ascii85: fix Decode with exact-size destination buffer

[alitavanaei98-droid]

Decode required four spare bytes in dst before processing each input byte, which caused flush of a final short block to fail when dst was sized to the decoded output length. Check available space only when writing output bytes.

Fixes #75590

Change-Id: I1e4794405f4b16126b50891e792ff61a773ca9c9

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

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