message: fix for substring with unicode and negative offset
diff: #include "duckdb/storage/statistics/string_statistics.hpp"
  #include "duckdb/planner/expression/bound_function_expression.hpp"
  #include "utf8proc.hpp"
  +#include "duckdb/common/types/blob.hpp"
  namespace duckdb {
  @@ -138,6 +139,13 @@ string_t SubstringFun::SubstringUnicode(Vector &result, string_t input, int64_t
  }
  }
  }
  + while (!LengthFun::IsCharacter(input_data[start_pos])) {
  + start_pos++;
  + }
  + while (end_pos < input_size && !LengthFun::IsCharacter(input_data[end_pos])) {
  + end_pos++;
  + }
  +
  if (end_pos == DConstants::INVALID_INDEX) {
  return SubstringEmptyString(result);
  }
  