Don't load higher resolution textures than requested

[RunitaiLinden]

Description

The log file is full of "LLViewerTextureList::updateImagesCreateTextures : ONCE (3300th time seen): Texture will be downscaled immediately after loading."

This indicates a higher resolution image was loaded than was requested. Find the cause and eliminate it.

[RunitaiLinden]

Fixed in ExtraFPS

There was an "optimization" in the texture fetcher that would load a texture at full resolution if all the bytes were available. The viewer would also sometimes request a higher resolution image, then determine a lower resolution was desired before the higher resolution decode completes.

Fix was to adjust the logic so that we never decode a higher resolution than requested, and if a higher resolution decode than currently desired completes, don't use the high res version.

A future optimization might attempt to abort the request in progress if the viewer detects it doesn't want the higher resolution image before the decode is complete.

[sergiiiproductengine]

Failed QA.

Verified on the Second Life Release 7.1.11.12208292573 on Win10/OSX in the scope of https://github.com/secondlife/iqa/issues/409.

Looks like the issue reproducible on locations with a lot of people and related to avatars
(eg http://maps.secondlife.com/secondlife/Blue%20Moon%20Bay/179/65/25).

Please, see attached log:
SecondLife.log