Fix a check that was attempting to see if an object file was in memory.

Checking if an object file is in memory should use the ObjectFile::IsInMemory(), not test ObjectFile::BaseAddress(). ObjectFile::BaseAddress() is designed to be overridden by all classes and is for mach-o, ELF and COFF plug-ins. They find the header base adddress and return that as a section offset address. The default implementation of ObjectFile::BaseAddress() does try and make an Address() from the ObjectFile::m_memory_addr, but I switched it to a correct function call.

Differential Revision: https://reviews.llvm.org/D86122