Bug #12116 patch

sql/field.h:
  64-bit safe is_null with offset
sql/key.cc:
  64-bit safe is_null with offset

sql/field.h

@@ -185,6 +185,12 @@ class Field
     return test(record[(uint) (null_ptr - (uchar*) table->record[0])] &
 		null_bit);
   }
+  inline bool is_null_in_record_with_offset(my_ptrdiff_t offset)
+  {
+    if (!null_ptr)
+      return 0;
+    return test(null_ptr[offset] & null_bit);
+  }
   inline void set_null(int row_offset=0)
     { if (null_ptr) null_ptr[row_offset]|= null_bit; }
   inline void set_notnull(int row_offset=0)

sql/key.cc

@@ -473,8 +473,8 @@ int key_rec_cmp(void *key, byte *first_rec, byte *second_rec)
     if (key_part->null_bit)
     {
       /* The key_part can contain NULL values */
-      bool first_is_null= field->is_null(first_diff);
-      bool sec_is_null= field->is_null(sec_diff);
+      bool first_is_null= field->is_null_in_record_with_offset(first_diff);
+      bool sec_is_null= field->is_null_in_record_with_offset(sec_diff);
       /*
         NULL is smaller then everything so if first is NULL and the other
         not then we know that we should return -1 and for the opposite