If we generate more code than allowed by the --wasm-max-code-space flag,
the {WasmCodeManager::Commit} method will fail (via fatal error). The
DCHECK that was placed before that call checked for a related condition
though, and failed before the {Commit} method could fail.
By moving it after the call, we fix this issue.

Adding a test case for this seems to be involved, since that test would
crash the whole process (because of the fatal error). So it would have
to be a unittest such that we can use ASSERT_DEATH_IF_SUPPORTED. In
unittests though we don't yet have the infrastructure to create a
NativeModule (needed for the WasmCodeAllocator). Alternatively we could
add special testing methods (and a constructor) to the
WasmCodeAllocator, but I do not consider this worth the effort for this
little fix.

R=thibaudm@chromium.org

Bug: chromium:1124646
Change-Id: Ief09dfbd0a5b0b040fe9cf8a34e458d1d01dfacc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2390754
Auto-Submit: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69723}