Fix concurrency problem.
Before this commit, if acquisition was aborted by user before the imagetask had
passed through the conditional
`if ((epicsTimeDiffInSeconds(¤tAcqTime, &prevAcqTime) > maxAcqusitionTime)`, condition would evaluate to true
and raise a warning saying that the acquisition timed out, which is not true.
After this, condition evaluates to false and no alarm is raised.
Tested several acquisitions and this does not seem to compromise the control flow.
It seems to work both with internal and with external triggers.
Douglas Araujo