Merge #4235

4235: Make the text's color lerping safer r=def- a=Jupeyy

`@vainiovano` can you test this?

## Checklist

- [x] Tested the change ingame
- [ ] Provided screenshots if it is a visual change
- [ ] Tested in combination with possibly related configuration options
- [ ] Written a unit test if it works standalone, system.c especially
- [ ] Considered possible null pointers and out of bounds array indexing
- [ ] Changed no physics that affect existing maps
- [ ] Tested the change with [ASan+UBSan or valgrind's memcheck](https://github.com/ddnet/ddnet/#using-addresssanitizer--undefinedbehavioursanitizer-or-valgrinds-memcheck) (optional)


Co-authored-by: Jupeyy <jupjopjap@gmail.com>

data/shader/text.frag

@@ -30,5 +30,8 @@ void main()
 	float RealAlpha = (textOutlineFrag.a + textColor.a);
 	
 	// simply add the color we will loose through blending
-	FragClr = vec4(finalFragColor / RealAlpha, RealAlpha);
+	if(RealAlpha > 0.0)
+		FragClr = vec4(finalFragColor / RealAlpha, RealAlpha);
+	else
+		FragClr = vec4(0.0, 0.0, 0.0, 0.0);
 }