math/big: (*Rat).SetString with "1.770p02041010010011001001" crashes with "makeslice: len out of range" [1.15 backport]

[gopherbot]

@katiehockman requested issue #45910 to be considered for backport to the next 1.15 minor release.

@gopherbot please consider this for backport to 1.15 and 1.16 as this is a security issue.

[gopherbot]

Change https://golang.org/cl/321831 mentions this issue: [release-branch.go1.15] math/big: check for excessive exponents in Rat.SetString

[dmitshur]

Approving as a fix for a security issue. This backport applies to both 1.16 (#46306) and 1.15 (this issue).

[gopherbot]

Closed by merging df9ce19 to release-branch.go1.15.