ENH: Restore test for FixedWidthTextReader

The test and data existed, but the test was not in the CMakeLists.txt
file.

Change-Id: I0939f5bdde2f497bac756da2ce0e485f4052ce29
Merge topic 'Coverage_FixedWidthTextReader' into master

34ac668a ENH: Restore test for FixedWidthTextReader