tracker-extract-gstreamer: Fix compile warning
tracker-extract-gstreamer: Fix compile warning

https://bugzilla.gnome.org/show_bug.cgi?id=656419

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