Fix valgrind warning about mismatched new/delete

Mostly a hygienic fix.
Fix uninitialized read of Texture::_format

Discovered by valgrind.
Call sequence leading to the problem:
Urho3D::FontFace::LoadFaceTexture calls CreateFaceTexture() and right afterwards SetData()
SetData will call IsCompressed() at line 316, thus reading potentially garbage data.
For a minor performance improvement, do not mark AnimatedModel skinning dirty if it does not contain bones.
Merge remote-tracking branch 'remotes/nemerle/valgrind_fixes'
Added contributor credit.
Fixed UI bug where positioning a window to the left partially outside the screen would cause GetElementAt() to stop working on the window's layouted child elements.