Fix skybox debug draw

Skybox is rendered with a mesh that has only position, so it can't be used with generic shader. Fixes the log spam and correctly shows where the skybox tris are.

src/engine/renderer/tr_shade.cpp

@@ -3053,7 +3053,10 @@ void Tess_End()
 			// draw debugging stuff
 			if ( r_showTris->integer || r_showBatches->integer || ( r_showLightBatches->integer && ( tess.stageIteratorFunc == Tess_StageIteratorLighting ) ) )
 			{
-				DrawTris();
+				// Skybox triangle rendering is done in Tess_StageIteratorSky()
+				if ( tess.stageIteratorFunc != Tess_StageIteratorSky ) {
+					DrawTris();
+				}
 			}
 		}
 	}

src/engine/renderer/tr_sky.cpp

@@ -126,6 +126,23 @@ void Tess_StageIteratorSky()
 		Tess_DrawElements();
 	}
 
+	if ( r_showTris->integer ) {
+		GL_State( GLS_POLYMODE_LINE | GLS_DEPTHFUNC_ALWAYS );
+
+		// bind u_ColorMap
+		gl_skyboxShader->SetUniform_ColorMapCubeBindless(
+			GL_BindToTMU( 0, tr.whiteCubeImage )
+		);
+
+		// Only render the outer skybox outline at this stage
+		gl_skyboxShader->SetUniform_UseCloudMap( false );
+
+		// u_AlphaThreshold
+		gl_skyboxShader->SetUniform_AlphaTest( GLS_ATEST_NONE );
+
+		Tess_DrawElements();
+	}
+
 	// Only render clouds at these stages
 	gl_skyboxShader->SetUniform_UseCloudMap( true );
 	gl_skyboxShader->SetUniform_CloudHeight( tess.surfaceShader->sky.cloudHeight );