[3.2] Fix compile warnings in eos-vm-oc's memory.hpp, executor.cpp, and memory.cpp

[linh2931]

Resolve #612

Fix the following warnings. Please double check if my fixes for memory.cpp and executor.cpp do not break anything. Thanks.

.../libraries/chain/include/eosio/chain/webassembly/eos-vm-oc/memory.hpp:53:32: warning: comparison of integer expressions of different signedness: ‘long unsigned int’ and ‘int’ [-Wsign-compare]
   53 |       static_assert(-cb_offset == EOS_VM_OC_CONTROL_BLOCK_OFFSET, "EOS VM OC control block offset has slid out of place somehow");

.../libraries/chain/webassembly/runtimes/eos-vm-oc/memory.cpp: In constructor ‘eosio::chain::eosvmoc::memory::memory(uint64_t)’:
.../libraries/chain/webassembly/runtimes/eos-vm-oc/memory.cpp:37:25: warning: ‘last’ may be used uninitialized in this function [-Wmaybe-uninitialized]
   37 |    fullpage_base = last + memory_prologue_size;
      |                    ~~~~~^~~~~~~~~~~~~~~~~~~~~~

.../libraries/chain/webassembly/runtimes/eos-vm-oc/executor.cpp: In lambda function:
.../libraries/chain/webassembly/runtimes/eos-vm-oc/executor.cpp:227:42: warning: comparison of integer expressions of different signedness: ‘int64_t’ {aka ‘long  int’} and ‘uint64_t’ {aka ‘long unsigned int’} [-Wsign-compare]
  227 |       if(cb->current_linear_memory_pages > base_pages) {
      |          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~

[spoonincode]

typo introduced in to string here (EEOS)

[linh2931]

Thanks @spoonincode for your sharp eyes! Sorry for that.