Fix for bug #23762: partition.test fails (partition_hash, partition_pruning as well)

When partition pruning is used we have to initialize key_part->flag in the 
create_partition_index_descr() as it's checked in the get_mm_leaf().

sql/opt_range.cc

@@ -3237,6 +3237,11 @@ static bool create_partition_index_description(PART_PRUNE_PARAM *ppar)
 
     key_part->field=        (*field);
     key_part->image_type =  Field::itRAW;
+    /* 
+      We set keypart flag to 0 here as the only HA_PART_KEY_SEG is checked
+      in the RangeAnalysisModule.
+    */
+    key_part->flag=         0;
     /* We don't set key_parts->null_bit as it will not be used */
 
     ppar->is_part_keypart[part]= !in_subpart_fields;

sql/opt_range.h

@@ -26,7 +26,9 @@
 
 typedef struct st_key_part {
   uint16           key,part, store_length, length;
-  uint8            null_bit, flag;
+  uint8            null_bit;
+  /* Keypart flags (0 if partition pruning is used) */
+  uint8 flag;
   Field            *field;
   Field::imagetype image_type;
 } KEY_PART;