Revert "QRegularExpression: lock a mutex only if there's actual work to do"

Blunder -- two threads may step into this method together,
both see not studied, and both study (with one leaking its study data).

This reverts commit 5fbd787cf9a72621d66604a4898f06ea4365226e.

Change-Id: Ia746925abcad1e43adf4f6f1d495b018de022b07
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
tst_qlogging: put the test for QT_MESSAGE_PATTERN in a data function

Change-Id: I9130b91dfe6bf1ee22431a423ec2d2f9ad62144a
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Logging: fix support for %{time format} in QT_MESSAGE_PATTERN

This revert commit de1d5815c15ba1f944752cf7d441442efeb0accb which
wrongly fixed a typo. There is no typo because we use startsWith
with that constant.

Also added a test because the %{time} support was added in commit
93563952d00f865b73136f6a316ca2b8732db85f but the test was missing

Change-Id: Ic96e6f21f989ca3a2905ec6c89b93d2627b77b40
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>