qtest: Allow and ignore blank lines in input

qtest: Allow and ignore blank lines in input

Currently the code that reads the qtest protocol commands insists
that every input line has a command.  If it receives a line with
nothing but whitespace it will trip an assertion in
qtest_process_command().

This is a little awkward for the case where we are feeding qtest a
set of bug-reproduction commands via standard input or a file,
because it means you need to be careful not to leave a blank line at
the start or the end when cutting and pasting the command sequence
from a bug report.

Change the code to allow and ignore blank lines in the input.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-ID: <20251106151959.1088095-1-peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>