Fix GH-16326: Memory management is broken for bad dictionaries

We must not `efree()` `zend_string`s, since they may have a refcount
greater than one, and may even be interned.

W

Fix GH-16326: Memory management is broken for bad dictionaries

We must not `efree()` `zend_string`s, since they may have a refcount
greater than one, and may even be interned.

We also must not confuse `zend_string *` with `zend_string **`.

And we should play it safe by using `safe_emalloc()` to avoid
theoretical integer overflows.

We also simplify a bit, according to suggestions of @TimWolla.

Closes GH-16335.

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