[core] GetWorldToScreen() does not support current matrix from rlPushMatrix()

[aldrinmartoq]

Please, before submitting a new issue verify and check:

• I tested it on latest raylib version from master branch
• I checked there is no similar issue already reported
• My code has no errors or misuse of raylib

Issue description

Ok, now I've got two issues with GetWorldToScreen() with my modified example models_rlgl_full_solar_system.c:

A. Maybe related to #901, GetWorldToScreen also doesn't support the current matrix from rlPushMatrix(). This means that we cannot put a label above a planet without replicating rlPushMatrix functionality.
B. When zooming in, all planet labels began to disappear, but suddenly there is a point when GetWorldToScreen show planet labels AGAIN. That point is when the designated point in space is "behind us". In my opinion, that information is incorrect.

Environment

Latest macOS (Mojave 10.14.5) on a Macbook retina, tested on current raylib master branche and raylib-2.5.0 from homebrew.

Issue Screenshot

For A., just check that labels do not respect the rlPushMatrix transformation, particularly the "moon" label appears close to the sun instead to earth.

To replicate B., just zoom in with the mouse until the labels disappear and then appear again. Use ALT+MOUSE2 to confirm that planet labels appear when the designated point is behind (just look around in 360º).

Code Example

Please check PR #900, particularly:
https://github.com/aldrinmartoq/raylib/blob/solar-system-examples/examples/models/models_rlgl_full_solar_system.c

Thank you very much.

[raysan5]

Out of scope for the moment.