OSV-2021-1820 Heap-buffer-overflow in r_str_utf8_codepoint

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=48098 Crash type: Heap-buffer-overflow READ 1 Crash state: rstrutf8codepoint rstrcharfullwidth rstrlenutf8ansi...