Fix unreported wireframe opacity color blending broken

This was introduced by rBdb7d8281c5a2.

The color needs to be premultiplied as there is no blend mode and
the output color is replacing the framebuffer color & alpha.

source/blender/draw/engines/overlay/shaders/wireframe_vert.glsl

@@ -160,6 +160,7 @@ void main()
   finalColor.rgb = mix(rim_col, final_front_col, facing);
   finalColor.rgb = pow(finalColor.rgb, vec3(2.2));
   finalColor.a = wireOpacity;
+  finalColor.rgb *= wireOpacity;
 #endif
 
   /* Cull flat edges below threshold. */