Fixed truncation in rbr_column_type_mismatch_whitelist when log_colum…

…n_names is enabled

Summary:
When log_column_names is enabled a different method is called
for unpacking rows. This original fix in D25250610 (48daa11) did not fix this method.

Squash with D25250610 (48daa11)

Reviewed By: hermanlee

Differential Revision: D27275573

fbshipit-source-id: 9a7666a841b