Ruby: SEGV in parse_rat()

A crafted string can cause SEGVREAD memory access to 0x000000000000 when parsed as rational number - ruby 2.5.1p57 on Fedora 28 $ ruby -e 'Rational"2e-9942067"' -e:1: warning: in ab, b may be too big -e:1: BUG Segmentation fault at 0x0000000000000000 ruby 2.5.1p57 2018-03-29 revision 63029...