Resize vertex buffer if necessary in cf_mesh_update_vertex_data

[waldnercharles]

I don't know if this is the right way to do this. It solved my problem so I figured I'd open a PR to discuss. Would it be better to instead do something like a pow2 resize?

[RandyGaul]

Looks good, though I would agree yes, a 2x size would be a bit better. Go ahead and just double the size if this if-statement is hit. The default size is very small like 5mb, so I would expect for games with lots of sprites for this to get hit a few times before settling.