Problem was an errornous date that lead to end partition
was before the start, leading to a crash.

Solution was to check greater or equal instead of only
equal between start and end partition.

NOTE: partitioning pruning handles incorrect dates
differently than index lookup, which can give different
results in a partitioned table versus a non partitioned
table for queries having 'bad' dates in the where clause.

mysql-test/r/partition_pruning.result:
  Bug#40972: some sql execution lead the whole databse crashing
  
  Updated result file
mysql-test/t/partition_pruning.test:
  Bug#40972: some sql execution lead the whole databse crashing
  
  Added test.
sql/sql_partition.cc:
  Bug#40972: some sql execution lead the whole databse crashing
  
  There can be cases where the start/cur partition is greater
  than the end partition, so it must not continue, since that
  can lead to a crash.