MeshHandler: Fix weightsData dequantization error (#338)

fix(MeshHandler): fix `weightsData` dequantization error
In the Editor's serialization code, normalized weights are quantized as 5-bit UNORM values then packed as ints. This implies flooring - while the sum of the quantized values are guaranteed to be `31` this can lead to a loss of precision where the _de_quantized sum (div by 31 then sum) of weights is less than 1.0.
Such cases can be trivally reproduced by search, for example a tuple of (1,25,5) summed as (1/31+25/31+5/31) in _that exact order_ will yield 0.9999999999999999 instead of 1.0, and ((1/31+25/31+5/31) >= 1.0) will be falsey.
This PR implements the sum of weight with ints instead. Alternatively an epsilon value could be chosen, but this is what the player code does.

Author: mos9527

UnityPy/helpers/MeshHelper.py

@@ -567,7 +567,6 @@ def decompress_compressed_mesh(self):
         # Skin
         if m_CompressedMesh.m_Weights.m_NumItems > 0:
             weightsData = unpack_ints(m_CompressedMesh.m_Weights)
-            weightsData = [weight / 31 for weight in weightsData]
             boneIndicesData = unpack_ints(m_CompressedMesh.m_BoneIndices)
 
             vertexIndex = 0
@@ -580,14 +579,14 @@ def decompress_compressed_mesh(self):
             boneIndicesIterator = iter(boneIndicesData)
             for weight, boneIndex in zip(weightsData, boneIndicesIterator):
                 # read bone index and weight
-                boneWeights[vertexIndex][j] = weight
+                boneWeights[vertexIndex][j] = weight / 31
                 boneIndices[vertexIndex][j] = boneIndex
 
                 j += 1
                 sum += weight
 
                 # the weights add up to one, continue with the next vertex.
-                if sum >= 1.0:
+                if sum >= 31:
                     j = 4
                     # set weights and boneIndices to 0,
                     # already done on init