"perf hists browser: Support flat callchains" appears to have broken parent reporting

[Andres Freund <andres@anarazel.de>]

Hi,

4b3a3212233a - "perf hists browser: Support flat callchains" seems to
have broken callchain display in tui mode when using !flat mode, or at
least changed it in an unintended manner.

Llooking at the same perf.data file:
perf report --tui --no-children -g
before:
-   16.69%  swapper          [kernel.kallsyms]             [k] poll_idle
   - poll_idle
      + 16.65% cpuidle_enter_state
      + 0.04% cpuidle_enter
-    3.51%  swapper          [kernel.kallsyms]             [k] intel_idle
   - intel_idle
      + 3.49% cpuidle_enter_state
      + 0.03% cpuidle_enter
-    1.35%  postgres         postgres                      [.] hash_search_with_hash_value
   - hash_search_with_hash_value
      - 0.32% BufTableLookup
         + ReadBuffer_common
      - 0.18% LockAcquireExtended
         + 0.16% LockRelationOid
         + 0.02% XactLockTableInsert
      + 0.14% FetchPreparedStatement
      + 0.13% CreatePortal
      + 0.11% RelationIdGetRelation
      + 0.10% GetPortalByName
after:
-   16.69%  swapper          [kernel.kallsyms]             [k] poll_idle
     poll_idle
-    3.51%  swapper          [kernel.kallsyms]             [k] intel_idle
     intel_idle
-    1.35%  postgres         postgres                      [.] hash_search_with_hash_value
     hash_search_with_hash_value
-    1.18%  postgres         postgres                      [.] AllocSetAlloc
     AllocSetAlloc
-    0.85%  postgres         libc-2.22.so                  [.] __memcpy_sse2_unaligned
     __memcpy_sse2_unaligned

as you can see after the aforementioned commit there's only one level of
callers reported.

--stdio output isn't affected.

I can provide an example perf.data file, but it apears to reproduce with
just about any profile here.

Greetings,

Andres Freund