block/raw-posix: Only sync after successful preallocation

The loop which filled the file with zeroes may have been left early due
to an error. In that case, the fsync() should be skipped.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/raw-posix.c

@@ -1453,7 +1453,9 @@ static int raw_create(const char *filename, QemuOpts *opts, Error **errp)
             }
             left -= result;
         }
-        fsync(fd);
+        if (result >= 0) {
+            fsync(fd);
+        }
         g_free(buf);
         break;
     }