vtkPiecewiseFunction: actually assign a fallback SearchMethod

The `type` value that was just verified as out-of-range is still set
after the block, so instead update it so the single assignment at the
end is shared.

(cherry picked from commit 9c6c952e)

Common/DataModel/vtkPiecewiseFunction.cxx

@@ -1111,7 +1111,7 @@ void vtkPiecewiseFunction::SetCustomSearchMethod(int type)
     vtkGenericWarningMacro("enum out of scope, binary search will be applied");
 
     // set to binary search because it is the most general searchMethod
-    this->Internal->CustomSearchMethod = BINARY_SEARCH;
+    type = BINARY_SEARCH;
   }
 
   this->Internal->CustomSearchMethod = static_cast<SearchMethod>(type);