Strokes are not rendered in some installations of Manim using OpenGL renderer

Nobody has claimed this yet.

## Description of bug / unexpected behavior
```
from manim import *
from manim.opengl import *

class Test(Scene):
def construct(self):
circle = OpenGLCircle()
circle.set_fill(BLUE, opacity=0.5)
circle.set_stroke(BLUE_E, width=4)
square = OpenGLSquare(fill_opacity=0, stroke_opacity=1, stroke_color=RED, stroke_width=5, draw_stroke_behind_fill=False)

self.play(FadeIn(square))
self.wait()

```
Gives a blank black screen:

https://user-images.githubusercontent.com/9102529/113471180-40006780-948d-11eb-88f6-38218c3f2ffe.mp4

While
```
from manim import *
from manim.opengl import *

class Test(Scene):
def construct(self):
circle = OpenGLCircle()
circle.set_fill(BLUE, opacity=0.5)
circle.set_stroke(BLUE_E, width=4)
square = OpenGLSquare(fill_opacity=1, stroke_opacity=1, stroke_color=RED, stroke_width=5, draw_stroke_behind_fill=False)

self.play(FadeIn(square))
self.wait()

```

Gives this:

https://user-images.githubusercontent.com/9102529/113471210-88b82080-948d-11eb-8330-0a17f7c3915e.mp4

This shows that the problem in my local installation lies with rendering strokes.

## Expected behavior
Strokes should render correctly.

## How to reproduce the issue

Code for reproducing the problem

```py
Paste your code here.
```

## Additional media files

Images/GIFs

## Logs
Terminal output

```
PASTE HERE OR PROVIDE LINK TO https://pastebin.com/ OR SIMILAR
```

## System specifications

System Details

- OS Microsoft Windows 10 Home Insider Preview Version10.0.21343 Build 21343
- RAM: Is this relevant?
- Python version (`python/py/python3 --version`): Python 3.9.2
- Installed modules (provide output from `pip list`):
```
Package Version
----------------------------- -----------
alabaster 0.7.12
ansicon 1.89.0
anyio 2.2.0
appdirs 1.4.4
argon2-cffi 20.1.0
astroid 2.5.2
async-generator 1.10
attrs 20.3.0
Babel 2.9.0
backcall 0.2.0
bleach 3.3.0
blessed 1.18.0
certifi 2020.12.5
cffi 1.14.5
chardet 4.0.0
colorama 0.4.4
colour 0.1.5
commonmark 0.9.1
decorator 4.4.2
defusedxml 0.7.0
dnspython 1.16.0
docopt 0.6.2
docutils 0.16
entrypoints 0.3
fett 0.3.2
flyingcircus 0.1.3.2
glcontext 2.3.3
grpcio 1.33.2
grpcio-tools 1.33.2
idna 2.10
imagesize 1.2.0
ipykernel 5.5.0
ipython 7.21.0
ipython-genutils 0.2.0
isort 5.8.0
jedi 0.18.0
Jinja2 2.11.3
jinxed 1.0.1
json5 0.9.5
jsonschema 3.2.0
jupyter-client 6.1.11
jupyter-core 4.7.1
jupyter-packaging 0.7.12
jupyter-server 1.4.1
jupyterlab 3.0.9
jupyterlab-pygments 0.1.2
jupyterlab-server 2.3.0
lazy-object-proxy 1.6.0
livereload 2.6.3
manim 0.5.0
ManimPango 0.2.4
mapbox-earcut 0.12.10
MarkupSafe 1.1.1
mccabe 0.6.1
mistune 0.8.4
moderngl 5.6.4
moderngl-window 2.3.0
multipledispatch 0.6.0
nbclassic 0.2.6
nbclient 0.5.3
nbconvert 6.0.7
nbformat 5.1.2
nest-asyncio 1.5.1
networkx 2.5
notebook 6.2.0
numpy 1.20.1
packaging 20.9
pandocfilters 1.4.3
parso 0.8.1
pickleshare 0.7.5
Pillow 8.1.0
pip 21.0.1
prometheus-client 0.9.0
prompt-toolkit 3.0.16
protobuf 3.15.5
pycairo 1.20.0
pycparser 2.20
pydub 0.24.1
pyglet 1.5.15
Pygments 2.8.0
pylint 2.7.3
pymongo 3.11.3
pyparsing 2.4.7
pyrr 0.10.3
pyrsistent 0.17.3
python-dateutil 2.8.1
python-jsonrpc-server 0.3.4
pytk 0.0.2.1
pytz 2021.1
pywin32 300
pywinpty 0.5.7
PyYAML 5.4.1
pyzmq 22.0.3
requests 2.25.1
rich 6.2.0
rstcheck 3.3.1
scipy 1.6.1
Send2Trash 1.5.0
setuptools 53.1.0
setuptools-scm 5.0.2
six 1.15.0
sniffio 1.2.0
snooty-lextudio 1.8.10.dev0
snowballstemmer 2.1.0
Sphinx 3.5.3
sphinx-autobuild 2021.3.14
sphinxcontrib-applehelp 1.0.2
sphinxcontrib-devhelp 1.0.2
sphinxcontrib-htmlhelp 1.0.3
sphinxcontrib-jsmath 1.0.1
sphinxcontrib-qthelp 1.0.3
sphinxcontrib-serializinghtml 1.1.4
terminado 0.9.2
testpath 0.4.4
toml 0.10.2
tornado 6.1
tqdm 4.58.0
traitlets 5.0.5
typing-extensions 3.7.4.3
urllib3 1.26.3
watchdog 1.0.2
wcwidth 0.2.5
webencodings 0.5.1
wheel 0.36.2
wrapt 1.12.1
```

LaTeX details

+ LaTeX distribution (e.g. TeX Live 2020):
+ Installed LaTeX packages:

FFMPEG

Output of `ffmpeg -version`:

```

```

## Additional comments

Start by running the provided Test scene with the OpenGL renderer, comparing the OpenGLSquare cases on the reported Windows 10 and Python 3.9.2 setup. Investigate the OpenGL stroke-rendering path and verify the reproduction after any change; done means the square's stroke renders correctly when fill_opacity is zero as well as when it is one.

Written by the indexing model from the issue text.