sparsefile: Initialize memory in unit test to make valgrind happy
sparsefile: Initialize memory in unit test to make valgrind happy

We were writing unitialized stack memory to the file.

mparis/gstreamer,krichter722/gstreamer,jpakkane/gstreamer,jpxiong/gstreamer,jpxiong/gstreamer,Lachann/gstreamer,surround-io/gstreamer,Lachann/gstreamer,mparis/gstreamer,krichter722/gstreamer,shelsonjava/gstreamer,shelsonjava/gstreamer,shelsonjava/gstreamer,Lachann/gstreamer,jpakkane/gstreamer,jpakkane/gstreamer,centricular/gstreamer,mparis/gstreamer,surround-io/gstreamer,mparis/gstreamer,centricular/gstreamer,jpxiong/gstreamer,krichter722/gstreamer,shelsonjava/gstreamer,krichter722/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,surround-io/gstreamer,mparis/gstreamer,centricular/gstreamer,jpxiong/gstreamer,jpxiong/gstreamer,jpakkane/gstreamer,jpakkane/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,surround-io/gstreamer,StreamUtils/gstreamer,surround-io/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,Lachann/gstreamer,shelsonjava/gstreamer,Lachann/gstreamer