Override monitors' lightmap coordinates

Shaders appear to ignore all the other subtle (and not-so-subtle) hints
we drop that monitors shouldn't be rendered with shadows. This solution
isn't optimal, as monitors may still be tinted due to sunlight, but
there is nothing we can do about that.

Many thanks to ferreusveritas for their help in diagnosing, fixing and
testing this issue.

Author: SquidDev

src/main/java/dan200/computercraft/client/render/TileEntityMonitorRenderer.java

@@ -18,6 +18,7 @@
 import net.minecraft.client.Minecraft;
 import net.minecraft.client.renderer.BufferBuilder;
 import net.minecraft.client.renderer.GlStateManager;
+import net.minecraft.client.renderer.OpenGlHelper;
 import net.minecraft.client.renderer.Tessellator;
 import net.minecraft.client.renderer.tileentity.TileEntitySpecialRenderer;
 import net.minecraft.client.renderer.vertex.DefaultVertexFormats;
@@ -97,6 +98,7 @@ private void renderMonitorAt( TileMonitor monitor, double posX, double posY, dou
 
             // Draw the contents
             GlStateManager.depthMask( false );
+            OpenGlHelper.setLightmapTextureCoords( OpenGlHelper.lightmapTexUnit, 0xFF, 0xFF );
             GlStateManager.disableLighting();
             mc.entityRenderer.disableLightmap();
             try