Jonah Williams f0a3cbace3
[flutter_tools] handle FileSystemException thrown when attempting to decode stamp file (#64559)
Fixes #64246

If decoding the string contents of a stamp file fails, treat it as if the stamp file is missing. This is always safe to do, since at worst it downloads more artifacts. The files could end up corrupted if they were edited by another program, for example
2020-08-25 10:58:21 -07:00
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