* Fix RETHROW handler missing IS_INVALID_TAGINDEX check
Add validation for exception_tag_index in the RETHROW opcode handler
to prevent out-of-bounds access to module->module->tags[] when the
tag index is INVALID_TAGINDEX (0xFFFFFFFF). This matches the existing
check in the THROW handler.
When CATCH_ALL catches a cross-module exception with an unknown tag,
it pushes INVALID_TAGINDEX onto the stack. Without this check, a
subsequent RETHROW would access tags[0xFFFFFFFF].
* Fix incorrect code section byte counts in exception handling test
The hand-crafted WASM binary in load_module_with_exception_handling had
an off-by-one in the code section: body size was declared as 7 but the
actual body (local count + try/catch_all/end/end) is only 6 bytes.
This caused the WASM loader to fail with "unexpected end" when it tried
to read past the available bytes.
Fix the body size from 7 to 6 and the code section size from 9 to 8.
