encoding/pem: malformed line endings can cause panics [1.25 backport]

[gopherbot]

@rolandshoemaker requested issue #76027 to be considered for backport to the next 1.25 minor release.

@gopherbot please open backports, this is a regression in PEM decoding.

[gopherbot]

Change https://go.dev/cl/714661 mentions this issue: [release-branch.go1.25] encoding/pem: properly calculate end indexes

[mknyszek]

Approved. The fix is small and simple and fixes a panic which has no convenient workaround.

[gopherbot]

Closed by merging CL 714661 (commit 83885f3) to release-branch.go1.25.

[dolmen]

The prefix of the title of this issue should be encoding/pem instead of pem/encoding.