Prevent panic when QueryAllocatedBlocks result empty

[ReLium]

Handle properly empty result from C.QueryAllocatedBlocks call in QueryAllocatedBlocks

[vmwclabot]

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[vmwclabot]

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[ReLium]

Currently empty response produces panic, because we ca't access [0] element in empty slice.

[vmwclabot]

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[ReLium]

@lintongj Please take a look :-)