Fixed usage of proxy textures on GLES2 sky

(cherry picked from commit eed4655644986c6e7e1957a08fbd8b1ef4bc0af1)

drivers/gles2/rasterizer_scene_gles2.cpp

@@ -2639,6 +2639,8 @@ void RasterizerSceneGLES2::_draw_sky(RasterizerStorageGLES2::Sky *p_sky, const C
 	RasterizerStorageGLES2::Texture *tex = storage->texture_owner.getornull(p_sky->panorama);
 	ERR_FAIL_COND(!tex);
 
+	tex = tex->get_ptr(); //resolve for proxies
+
 	glActiveTexture(GL_TEXTURE0);
 	glBindTexture(tex->target, tex->tex_id);
 

drivers/gles2/rasterizer_storage_gles2.cpp

@@ -1229,6 +1229,8 @@ void RasterizerStorageGLES2::sky_set_texture(RID p_sky, RID p_panorama, int p_ra
 		ERR_FAIL_COND(!texture);
 	}
 
+	texture = texture->get_ptr(); //resolve for proxies
+
 	// glBindVertexArray(0) and more
 	{
 		glBindBuffer(GL_ARRAY_BUFFER, 0);