tracker-extract: Fix initialization of error variable to NULL
tracker-extract: Fix initialization of error variable to NULL

hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker