Describe the bug
Unchecked error when reading all data from reader in decodePart() function at fetcher/fetcher.go:138. The result is assigned to _, _ which silently ignores potential read failures.

To reproduce

1. Trigger decodePart() with failing reader
2. Error is silently ignored
3. Partial or corrupt data may be returned

Expected behavior
Should check error and return it to caller

Matcha version
master branch

OS
All

Additional context
File: fetcher/fetcher.go line 138
Pattern: body, _ := ioutil.ReadAll(reader) with ignored error