check buffer size before reading BOM in setupInputStream - #235
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setupInputStream in runtime/C/src/antlr3filestream.c peeks at the first two to four bytes of the input to detect a UTF-8/UTF-16/UTF-32 byte order mark, but it dereferences nextChar[0..3] without ever consulting input->sizeBuf, so opening a file or string stream that is shorter than the BOM under one of those encodings reads past the end of the buffer. A 1-byte input whose first byte matches a BOM lead byte is enough to trigger a heap over-read under ASan. I added an input->sizeBuf length check in front of each BOM comparison, which is where the read happens and where every other reader in the runtime already bounds-checks against data + sizeBuf, so a short buffer just skips BOM detection. Worth verifying that valid BOMs still get consumed: a proper UTF-16 BOM still advances two bytes and a UTF-8 BOM three.