Fix out-of-range error (MSVC2010) in idl_gen_dart.cpp (#5335)
Fix out-of-range error (MSVC2010) in idl_gen_dart.cpp (#5335)

-- MSVC2010 doesn't support indexed access to \0-terminator.
alexames/flatbuffers,pjulien/flatbuffers,alexames/flatbuffers,stewartmiles/flatbuffers,google/flatbuffers,alexames/flatbuffers,evolutional/flatbuffers,pjulien/flatbuffers,stewartmiles/flatbuffers,stewartmiles/flatbuffers,stewartmiles/flatbuffers,stewartmiles/flatbuffers,pjulien/flatbuffers,DavadDi/flatbuffers,pjulien/flatbuffers,pjulien/flatbuffers,stewartmiles/flatbuffers,royalharsh/flatbuffers,alexames/flatbuffers,evolutional/flatbuffers,google/flatbuffers,royalharsh/flatbuffers,royalharsh/flatbuffers,google/flatbuffers,royalharsh/flatbuffers,google/flatbuffers,google/flatbuffers,google/flatbuffers,pjulien/flatbuffers,stewartmiles/flatbuffers,evolutional/flatbuffers,alexames/flatbuffers,pjulien/flatbuffers,google/flatbuffers,google/flatbuffers,evolutional/flatbuffers,google/flatbuffers,alexames/flatbuffers,alexames/flatbuffers,royalharsh/flatbuffers,alexames/flatbuffers,google/flatbuffers,alexames/flatbuffers,evolutional/flatbuffers,stewartmiles/flatbuffers,royalharsh/flatbuffers,evolutional/flatbuffers,DavadDi/flatbuffers,alexames/flatbuffers,google/flatbuffers,evolutional/flatbuffers,DavadDi/flatbuffers,royalharsh/flatbuffers,evolutional/flatbuffers,stewartmiles/flatbuffers,royalharsh/flatbuffers,alexames/flatbuffers,evolutional/flatbuffers,stewartmiles/flatbuffers,alexames/flatbuffers,evolutional/flatbuffers,evolutional/flatbuffers,stewartmiles/flatbuffers,pjulien/flatbuffers,pjulien/flatbuffers,google/flatbuffers,stewartmiles/flatbuffers,google/flatbuffers,pjulien/flatbuffers,royalharsh/flatbuffers,DavadDi/flatbuffers,DavadDi/flatbuffers,google/flatbuffers,evolutional/flatbuffers,DavadDi/flatbuffers,pjulien/flatbuffers,alexames/flatbuffers,alexames/flatbuffers,alexames/flatbuffers,google/flatbuffers,pjulien/flatbuffers,stewartmiles/flatbuffers,royalharsh/flatbuffers,evolutional/flatbuffers