EditMesh: Fix uninitialized value causing red outline on edges

source/blender/draw/modes/shaders/edit_mesh_overlay_geom_tri.glsl

@@ -167,6 +167,8 @@ void main()
 	/* Remember that we are assuming the last vertex
 	 * of a triangle is the provoking vertex (decide what flat attribs are). */
 
+	flag = eflag;
+
 	if ((eflag[2] & EDGE_EXISTS) != 0) {
 		/* Do 0 -> 1 edge strip */
 		faceColor = vec4(fcol.rgb, 0.0);