Fix regression with CSS fallback renderer.

Regression caused rendering issue for cubemaps (but not multires) when CSS
fallback render was used. The regression was introduced as an optimization in
5eab5366f6.

src/js/libpannellum.js

@@ -45,6 +45,7 @@ function Renderer(container) {
     var texCoordBuffer, cubeVertBuf, cubeVertTexCoordBuf, cubeVertIndBuf;
     var globalParams;
     var sides = ['f', 'b', 'u', 'd', 'l', 'r'];
+    var fallbackSides = ['f', 'r', 'b', 'l', 'u', 'd'];
 
     /**
      * Initialize renderer.
@@ -205,7 +206,7 @@ function Renderer(container) {
             var onLoad = function() {
                 // Draw image on canvas
                 var faceCanvas = document.createElement('canvas');
-                faceCanvas.className = 'pnlm-face pnlm-' + sides[this.side] + 'face';
+                faceCanvas.className = 'pnlm-face pnlm-' + fallbackSides[this.side] + 'face';
                 world.appendChild(faceCanvas);
                 var faceContext = faceCanvas.getContext('2d');
                 faceCanvas.style.width = this.width + 4 + 'px';
@@ -284,7 +285,7 @@ function Renderer(container) {
                 faceImg.onload = onLoad;
                 faceImg.onerror = incLoaded; // ignore missing face to support partial fallback image
                 if (imageType == 'multires') {
-                    faceImg.src = path.replace('%s', sides[s]) + '.' + image.extension;
+                    faceImg.src = path.replace('%s', fallbackSides[s]) + '.' + image.extension;
                 } else {
                     faceImg.src = image[s].src;
                 }