LibWasm: Fix memarg multi-memory reading #883

Job	Run time
Lagom (Linux, ubuntu-22.04, NO_FUZZ) / CI	17m 50s
Lagom (Linux, ubuntu-22.04, FUZZ) / CI	11m 30s
SerenityOS (Clang, ubuntu-22.04, x86_64, NORMAL_DEBUG) / CI	9m 25s
Lagom (macOS, macos-14, NO_FUZZ) / CI	23m 56s
SerenityOS (GNU, ubuntu-22.04, aarch64, NORMAL_DEBUG) / CI	12m 27s
SerenityOS (GNU, ubuntu-22.04, x86_64, ALL_DEBUG) / CI	13m 12s
SerenityOS (GNU, ubuntu-22.04, x86_64, NORMAL_DEBUG) / CI	9m 33s
	1h 37m 53s

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