Don't allocate resize buffer for texture upload if the texture does not need to be...

Don't allocate resize buffer for texture upload if the texture does not need to be resized (this helps with memory pressure on the bouncegrid texture which was causing a huge memory alloc every frame in dynamic mode).

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@12296 d7cf8633-e32d-0410-b094-e92efae38249