ui-clone.c: Fix path check

The starts_with() check was broken in two ways: For one thing, the
parameters were passed in the wrong order, for another thing,
starts_with() returns 1 if the string starts with the prefix (not 0).

Note that this bug existed since commit 02a545e (Add support for cloning
over http, 2008-08-06) but only pops in in corner cases.

Signed-off-by: Lukas Fleischer <cgit@cryptocrack.de>