Include assert.h in range_encoder.h

[Moisan]

Building precomp on MacOS Sonoma leads to the following error

precomp-cpp-0.4.7/contrib/liblzma/rangecoder/range_encoder.h:153:2: error: call to undeclared function 'assert'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
        assert(rc->count <= RC_SYMBOLS_MAX);
        ^

This PR fixes the issue by adding #include <assert.h> in range_encoder.h.