testlib: executing a test with an invalid data label doesn't count as a failure and doesn't return a non-zero exit code

user@host:~/build/qt5/qtbase/tests/auto/testlib/selftests$ counting/counting testPassPass:foobar
********* Start testing of tst_Counting *********
Config: Using QTest library 5.0.0, Qt 5.0.0
PASS   : tst_Counting::initTestCase()
Unknown testdata for function testPassPass(): 'foobar'
Available testdata:
row 1
row 2
PASS   : tst_Counting::cleanupTestCase()
Totals: 2 passed, 0 failed, 0 skipped
********* Finished testing of tst_Counting *********
user@host:~/build/qt5/qtbase/tests/auto/testlib/selftests$ echo $?
0