internal/profile: actually return errors in postDecode

As spotted by staticcheck, the body did keep track of errors by sharing
a single err variable, but its last value was never used as the function
simply finished by returning nil.

To prevent postDecode from erroring on empty profiles,
which breaks TestEmptyProfile, add a check at the top of the function.

Update the runtime/pprof test accordingly,
since the default units didn't make sense for an empty profile anyway.

Change-Id: I188cd8337434adf9169651ab5c914731b8b20f39
Reviewed-on: https://go-review.googlesource.com/c/go/+/483137
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

0 files changed, 0 insertions, 0 deletions