media: v4l2-tpg: prevent the risk of a division by zero

In the Linux kernel, the following vulnerability has been resolved: media: v4l2-tpg: prevent the risk of a division by zero As reported by Coverity, the logic at tpg_precalculate_line() blindly rescales the buffer even when scaled_witdh is equal to zero. If this ever happens, this will cause a division by zero. Instead, add a WARN_ON_ONCE() to trigger such cases and return without doing any precalculation.