text/template: panics on method on nil interface value [1.12 backport]

[gopherbot]

@mvdan requested issue #30143 to be considered for backport to the next 1.12 minor release.

@gopherbot please backport to 1.12

[gopherbot]

Change https://golang.org/cl/164457 mentions this issue: [release-branch.go1.12] text/template: error on method calls on nil interfaces

[julieqiu]

@mvdan - there isn't a reason provided in the gopherbot message. Would you mind providing one for this backport?

[mvdan]

We fixed one set of panics when making template calls, but forgot some others. This makes 1.12 more consistent in handling panics during template calls.

Is there a convention to add the reason for the backport in the backport issue directly?

[gopherbot]

Closed by merging ad8ebb9 to release-branch.go1.12.