cmdQemuMonitorCommandQMPWrap: Reset ignored errors from JSON parsing

cmdQemuMonitorCommandQMPWrap: Reset ignored errors from JSON parsing

'cmdQemuMonitorCommandQMPWrap' is checking whether the user provided
string is not valid JSON to avoid wrapping it. In cases where it's not
JSON we ignore the error and add the wrapper.

If the caller then reports a different non-libvirt error the error from
the JSON parsing would be printed as well. Reset errors we ignore:

 # virsh qemu-monitor-command cd --pass-fds a asdf
 error: Unable to parse FD number 'a'
 error: internal error: cannot parse json asdf: lexical error: invalid char in json text.
                                        asdf
                      (right here) ------^

In the above case 'asdf' is not valid JSON, but the code did wrap it
into '{"execute":"asdf"}', the only problem is the argument for
--pass-fds.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>