Fix loading of GSAB length

Author: syg

spec.html

@@ -42598,7 +42598,9 @@ <h1>
         <emu-alg>
           1. If IsSharedArrayBuffer(_arrayBuffer_) is *true* and _arrayBuffer_ has an [[ArrayBufferByteLengthData]] internal slot, then
             1. Let _bufferByteLengthBlock_ be _arrayBuffer_.[[ArrayBufferByteLengthData]].
-            1. Return ℝ(GetValueFromBuffer(_bufferByteLengthBlock_, 0, ~BigUint64~, *true*, _order_)).
+            1. Let _rawLength_ be GetRawBytesFromSharedBlock(_bufferByteLengthBlock_, 0, ~BigUint64~, *true*, _order_).
+            1. Let _isLittleEndian_ be the value of the [[LittleEndian]] field of the surrounding agent's Agent Record.
+            1. Return ℝ(RawBytesToNumeric(~BigUint64~, _rawLength_, _isLittleEndian_)).
           1. Assert: IsDetachedBuffer(_arrayBuffer_) is *false*.
           1. Return _arrayBuffer_.[[ArrayBufferByteLength]].
         </emu-alg>