Change umovestr API: return > 0 instead of 0 if NUL was seen

Change umovestr API: return > 0 instead of 0 if NUL was seen

* pathtrace.c (upathmatch): Adjust umovestr return value check for new API.
* util.c (printpathn): Use umovestr() > 0 return value for more efficient
(and robust - we don't depend on "no overwrote past NUL" behavior anymore)
handling of terminating NUL.
(printstr): Remove useless NUL placement before umovestr() call.
Allocate 1 byte more to outstr[] array - for NUL.
(umovestr): Change to return 1 if NUL was seen.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>