Fix boolean conversion warnings

Fix boolean conversion warnings

Summary:

The compiler complains and raised some warnings about boolean
conversion:

    warning: address of 'ce->constants_table' will always evaluate to
    'true' [-Wpointer-bool-conversion]

Since the address of 'HashTable' will always evaluate to true. the
condition should be removed. The scope is kept for local variables.

Platform:

    OS X 10.11

Compiler:

    Apple LLVM version 7.0.0 (clang-700.0.72)
    Target: x86_64-apple-darwin15.0.0
    Thread model: posix