ctf: Take alignment into consideration for Strings too

ctf: Take alignment into consideration for Strings too

The alignment was not taken into consideration at all when reading
strings. It seemed to work so far for standardly-aligned fields, but
it stopped being the case with funky alignments.

This seems to fix bug #419536.

Change-Id: I4bbcb4dff2e8b68f0d86557d84b158131a9945d7
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/17438
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
IP-Clean: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>