Broken column titles for multiple measures using `layout=region`

[sjockers]

When combining multiple measures in one table and using layout=region, column titles for measures are broken (split by character using '.').

Example: https://tabular.genesapi.org/?parent=08&level=3&data=99910%3AAI0216&data=99910%3AAI0215&format=csv&time=2018&layout=region

region_id,A.I.0.2.1.5-year:2018,A.I.0.2.1.6-year:2018
08111,27.5,26.6
08115,33.0,33.2
08116,33.7,31.3
08117,36.3,32.2
(...)