imagemagickExec() blocking (forever) on Windows when cmd is wrong

The method ImageMagickToolkit::imagemagickExec() when executed on windows, uses a "'start' workaround" to prevent a cmd shell from popping up. However, if the executed commandline contains an error, e.g. pointing to a non existing executable. fgets($pipes[1]) will block the request and will never return. When the cmdline gets executed in a command prompt a error popup appears waiting to be clicked to be dismissed. Apparently the process will be waiting on a similar event in the above case which can never occur.

So we should try to get rid of this start workaround without getting a cmd prompt window popped up on each call to imagemagickExec().

I am still trying some alternatives, to come up with the best approach.
- just not using "start ... /B ..." works fine for me (and no window popping up, but I will dive deeper into the history of when and why it was added).
- the related issue mentions another possible solution.
- ... ??? (other approaches).

Note the related issue is for 7.x and so I did not want to hijack that one for a 8.x solution.