text/template: should `t.init()` be executed before `t.muTmpl.Lock()` in `AddParseTree()` method? [1.16 backport]

[gopherbot]

@ianlancetaylor requested issue #48436 to be considered for backport to the next 1.16 minor release.

@gopherbot Please open backports to 1.16 and 1.17

Fix regression in AddParseTree due to earlier fix for #39807.

[gopherbot]

Change https://golang.org/cl/351116 mentions this issue: [release-branch.go1.16] text/template: initialize template before locking it

[toothrot]

Approved. This is a serious issue with no workaround (and a regression).

[gopherbot]

Closed by merging 7d57324 to release-branch.go1.16.