Explain:
- problem: Delete and DeleteProxied could panic on malformed URLs when a JWT was provided.
- root cause: maybeAddAuth was called before checking the error returned by http.NewRequest, so req could be nil.
- fix: return the request construction error before adding the Authorization header.
- validation: go test ./weed/util/http -run 'TestDelete(ReturnsInvalidRequestErrorBeforeAddingAuth|ProxiedReturnsInvalidRequestErrorBeforeAddingAuth)' -count=1; git diff --check