Fix incorrect logging output.

commandArgsToString will already always start with a space so the extra
one was redundant and incorrect.

empty string arguments are also quoted for clarity (these empty strings
do get passed as actual arguments so this is good for debugging).

Change-Id: Iba1c825a4ce62544b4df5e554c9453d2d2e22b10
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>