Properly fail to parse lines of two or one chars

When we encountered e.g. a line with the contents 'c ', we did
not advance the char iterator to the end of the string and kept
it instead at the beginning of the line. Then, when we tried to
parse the timestamp, we would interpret the 'c' as 0xc == 12.
This then lead to breakage when we try to compute the chart model:
There, we would improperly use 12 as the maximum timestamp and
then essentially drop our time filter, instead trying to visualize
all charts and with wrong timestamps too.

This patch fixes this issue, we now fail to parse the 'c ' line
and thus simply omit the last timestamp and do not get confused
when building the chart model data.