Tools/MapExtractor: Fix string-related memory issues

Fix not-NULL terminated char buffers and char[] to string conversion.

Valgrind logs:
 Invalid read of size 1
  at 0x4C2D7D4: __GI_strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
  by 0x5318BAF: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, std::allocator<char> const&) (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.17)
  by 0x409471: ReadBuild(int) (System.cpp:189)
  by 0x40CEC6: main (System.cpp:1108)
  Address 0x5f851ee is 0 bytes after a block of size 94 alloc'd
  at 0x4C2C037: operator new[](unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
  by 0x40F63A: MPQFile::MPQFile(char const*) (mpq_libmpq.cpp:65)
  by 0x409408: ReadBuild(int) (System.cpp:182)
  by 0x40CEC6: main (System.cpp:1108)

 Invalid read of size 1
  at 0x57FFCAC: strtok (strtok.S:165)
  by 0x40D279: MPQArchive::GetFileListTo(std::vector<std::string, std::allocator<std::string> >&) (mpq_libmpq04.h:45)
  by 0x40C5CF: ExtractDBCFiles(int, bool) (System.cpp:1001)
  by 0x40CEF5: main (System.cpp:1110)
  Address 0x5f91e27 is 0 bytes after a block of size 44,391 alloc'd
  at 0x4C2C037: operator new[](unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
  by 0x40D1A5: MPQArchive::GetFileListTo(std::vector<std::string, std::allocator<std::string> >&) (mpq_libmpq04.h:30)
  by 0x40C5CF: ExtractDBCFiles(int, bool) (System.cpp:1001)
  by 0x40CEF5: main (System.cpp:1110)