'lock wait timeout exceeded'

Problem was a bug in the implementation of scan in partitioning
which masked the error code from the partition's handler.

Fixed by returning the value from the underlying handler.

mysql-test/suite/parts/r/partition_special_innodb.result:
  Bug#40515: Query on a partitioned table does not return
  'lock wait timeout exceeded'
  
  Updated test result
mysql-test/suite/parts/t/partition_special_innodb.test:
  Bug#40515: Query on a partitioned table does not return
  'lock wait timeout exceeded'
  
  Updated test case for covering the bug.
sql/ha_partition.cc:
  Bug#40515: Query on a partitioned table does not return
  'lock wait timeout exceeded'
  
  Removing redeclaration of result variable,
  which resulted in never returning the correct return value.