Use a null texture for incorrect render-to-texture + delete better

It seems it did cause problems in some games, so this:
 * Uses a smarter iterator to detach framebuffers more correctly.
 * Avoids binding framebuffers of the wrong format/etc.
 * Disables rendering of bad framebuffers (uses a null texture.)

This disables some of the bloom in Sword Art Online (some right, some wrong), and doesn't have any adverse affects on 3rd Birthday that I know of.  I'm hoping it will help other games negatively affected, as a temporary workaround.  No matter what, I don't like rendering garbage.

Note that this also skips rendering to a texture of a different format (but tries to use an FBO with the correct format if possible.)  This does happen, and I think it could possibly be keeping alive the incorrect framebuffer in some cases (since we allow to FBOs at the same address with different formats):

http://report.ppsspp.org/logs/kind/253

-[Unknown]