Fix flaky prefetcher unit tests

[rdpsin]

The prefetcher unit tests were failing because of uninitialized garbage
data when deserializing the dictionaries from the binary blob.

Signed-off-by: Rishabh Singhvi rdpsin@amazon.com

Issue #, if available:
Fixes #24

Description of changes:

Testing performed:

Before :

$ for i in {0..100}; do go clean -testcache; go test ./...; echo $?; done | grep 1 | wc -l
17

After:

$ for i in {0..100}; do go clean -testcache; go test ./...; echo $?; done | grep 1 | wc -l
0

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