Don't skip zero'ing end of volume file when inputvol is shorter than newvol

A missing set of braces around an error condition caused us to skip
zero'ing out the remainder of a new volume file if the new volume was
longer than the original (the goto was supposed to be taken only in
the case of error, but was always being taken).

src/storage/storage_backend.c

@@ -288,9 +288,10 @@ static int createRawFileOpHook(int fd, void *data) {
     if (hdata->inputvol) {
         int res = virStorageBackendCopyToFD(hdata->vol, hdata->inputvol,
                                             fd, &remain, 1);
-        if (res < 0)
+        if (res < 0) {
             ret = -res;
             goto cleanup;
+        }
     }
 
     if (remain) {