Fix memory allocation for test data.

Previously it seems to have worked by accident (there was not enough
space for the end NULL byte).

videohubctrl.c

 				f = fopen(optarg, "r");
 				if (!f)
 					die("Can't open %s: %s", optarg, strerror(errno));
-				test_data = xzalloc(st.st_size);
+				test_data = xzalloc(st.st_size + 1);
 				if (fread(test_data, st.st_size, 1, f) < 1)
 					die("Can't read from %s: %s", optarg, strerror(errno));
 				fclose(f);