Fixed the bug, where the dude falls through blocks.

When fps rate drops very low(e.g. through moving the application window
very fast) the dude would fall through blocks, because the deltaTime
gets huge and the collision detection would predict the dudes position
below the block directly below the dude.
By clamping the delta time to a defined minimum value(currently 0.2f <=>
5 fps) this doesn't happen.