[BUG] - Sometimes crash on macOS

[lucasjinreal]

When inputting, sometimes will crash (perhaps with probability of 40%). input with Chinese specifically.

Any chances to have a test?

Thread 0 Crashed:: (input method 18934 com.apple.inputmethod.SCIM) Dispatch queue: com.apple.main-thread
0   libsystem_kernel.dylib        	       0x18c713720 __pthread_kill + 8
1   libsystem_pthread.dylib       	       0x18c74bf70 pthread_kill + 288
2   libsystem_c.dylib             	       0x18c658908 abort + 128
3   FlutterMacOS                  	       0x1075cf718 std::_fl::__throw_out_of_range[abi:v15000](char const*) + 4 (stdexcept:271) [inlined]
4   FlutterMacOS                  	       0x1075cf718 std::_fl::basic_string<char16_t, std::_fl::char_traits<char16_t>, std::_fl::allocator<char16_t>>::__throw_out_of_range[abi:v15000]() const + 4 (string:1809) [inlined]
5   FlutterMacOS                  	       0x1075cf718 std::_fl::basic_string<char16_t, std::_fl::char_traits<char16_t>, std::_fl::allocator<char16_t>>::replace(unsigned long, unsigned long, char16_t const*, unsigned long) + 488 (string:3073)
6   FlutterMacOS                  	       0x1075d072c std::_fl::basic_string<char16_t, std::_fl::char_traits<char16_t>, std::_fl::allocator<char16_t>>::replace(unsigned long, unsigned long, std::_fl::basic_string<char16_t, std::_fl::char_traits<char16_t>, std::_fl::allocator<char16_t>> const&) + 8 (string:3168) [inlined]