Bug 15290: SQL reports headers encoding problem

Bug 15290: SQL reports headers encoding problem

To test:

- Create an SQL report with column names containing UTF characters
- Run the report
=> FAIL: The column names are double encoded
- Export the report
=> FAIL: The column names are double encoded in the exported file
- Apply the patch
- Re-run the report (reload works)
=> SUCCESS: Encoding correct
- Export the report
=> SUCCESS: Encoding correct
- Sign off :-D

Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 879b1386ff3a274d0884dc0b48afa6064c35eed7)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>