Fix T74800 Bevel modifier generates vertex group weight > 1.0.

Due to floating point approximations, the weights for interpolating
the mdeformvert layer could add up to a tiny bit more than 1.0.
This was not a problem in practice, but the mesh validation routine
used in regression tests was testing for this and therefore failing.
Just changed interpolation of mdeformverts to clamp max to 1.0f.

source/blender/blenkernel/intern/customdata.c

@@ -315,6 +315,9 @@ static void layerInterp_mdeformvert(const void **sources,
   if (totweight) {
     dvert->totweight = totweight;
     for (i = 0, node = dest_dwlink; node; node = node->next, i++) {
+      if (node->dw.weight > 1.0f) {
+        node->dw.weight = 1.0f;
+      }
       dvert->dw[i] = node->dw;
     }
   }