Code like:

if( aCommandURL.copy(5) != ".uno:" )

is obviously wrong, as OUString::copy(sal_Int32) takes the _beginning_
index, so for this condition to be false the command URL must have
".uno:" in the _middle_ of the string. This created some weird things
like an empty label attribute added to any submenu item. Moreover, the
command URL can be easily shorter than 5 (like when a custom submenu
added by the user). Using copy(5) in such case officially considered as
"undefined behavior" and will trigger an assert in debug build (that's
how I discovered this code actually).

Most likely the original intent was to check whether the command URL
doesn't start with ".uno:", and so should be changed to use
OUString::startsWith. But doing that will create a regression, as it
won't be possible anymore to change labels of commands that start with
".uno:". Simply dropping this check seems to be better solution here.

Change-Id: I2f88807eceae1006066a14750f2003e235f49ad4