Cache when not found in LookupLayout

Very visible when using the pprof mutex profiler.

```bash
name         old time/op    new time/op    delta
Baseline-10    58.4ms ± 1%    51.6ms ± 0%  -11.56%  (p=0.029 n=4+4)

name         old alloc/op   new alloc/op   delta
Baseline-10    64.3MB ± 0%    64.2MB ± 0%     ~     (p=0.114 n=4+4)

name         old allocs/op  new allocs/op  delta
Baseline-10      649k ± 0%      649k ± 0%     ~     (p=0.229 n=4+4)
```

0 files changed, 0 insertions, 0 deletions