GetActive() seg faults in very very corner case once in a while

[sreedharani]

When a cache.Refresh() followed by GetActive() is done on a deleted object, it occasionally results in a segfault like below. The root cause is the entry is not validated before getInvalidated() is performed on it

panic: runtime error: invalid memory address or nil pointer dereference [recovered]
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x15ce765]
....
....
/usr/local/go/src/runtime/panic.go:914 +0x21f
github.com/Comcast/goburrow-cache.(*entry).getInvalidated(...)
/Users/soggu464/go/pkg/mod/github.com/!comcast/goburrow-cache@v1.0.3/policy.go:90
github.com/Comcast/goburrow-cache.(*localCache).GetActive(0xc000110780,
/Users/soggu464/go/pkg/mod/github.com/!comcast/goburrow-cache@v1.0.3/local.go:198 +0x65…

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