thrift/lib/cpp2/protocol/CompactProtocol-inl.h: fix -Wimplicit-int-conversion
thrift/lib/cpp2/protocol/CompactProtocol-inl.h: fix -Wimplicit-int-conversion

Reviewed By: luciang

Differential Revision: D34120915

fbshipit-source-id: b8c154f9603d72680e7ac4ed6bd48cf3a0a2c40e

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift