backport of Bug#11867664 from mysql-5.5

 3381 Mattias Jonsson	2011-03-18
      Bug#11867664:  SERVER CRASHES ON UPDATE WITH JOIN ON PARTITIONED TABLE
      
      Regression from bug#11766232.
      m_last_part could be set beyond the last partition.
      Fixed by only setting it if within the limit.
      Also added check in print_error.

sql/ha_partition.cc

@@ -4317,7 +4317,8 @@ int ha_partition::index_read_idx_map(uchar *buf, uint index,
           break;
       }
     }
-    m_last_part= part;
+    if (part <= m_part_spec.end_part)
+      m_last_part= part;
   }
   else
   {
@@ -6237,7 +6238,14 @@ void ha_partition::print_error(int error, myf errflag)
   {
     /* In case m_file has not been initialized, like in bug#42438 */
     if (m_file)
+    {
+      if (m_last_part >= m_tot_parts)
+      {
+        DBUG_ASSERT(0);
+        m_last_part= 0;
+      }
       m_file[m_last_part]->print_error(error, errflag);
+    }
     else
       handler::print_error(error, errflag);
   }