Fix GH-15905: Assertion failure for TRACK_VARS_SERVER

When the superglobals are eagerly initialized, but "S" is not contained
in `variables_order`, `TRACK_VARS_SERVER` is created as empt

Fix GH-15905: Assertion failure for TRACK_VARS_SERVER

When the superglobals are eagerly initialized, but "S" is not contained
in `variables_order`, `TRACK_VARS_SERVER` is created as empty array
with refcount > 1. Since this hash table may later be modified, a flag
is set which allows such COW violations for assertions. However, when
`register_argc_argv` is on, the so far uninitialized hash table is
updated with `argv`, what causes the hash table to be initialized, what
drops the allow-COW-violations flag. The following update with `argc`
then triggers a refcount violation assertion.

Since we consider `HT_ALLOW_COW_VIOLATION` a hack, we do not want to
keep the flag during hash table initialization, so we initialize the
hash table right away after creation for this code path.

Closes GH-15930.

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