[Fix] Improve handling of lost device on WebGL (playcanvas#7121)

Co-authored-by: Martin Valigursky <mvaligursky@snapchat.com>

Author: mvaligursky

src/platform/graphics/webgl/webgl-shader.js

@@ -192,12 +192,17 @@ class WebglShader {
      * @param {string} src - The shader source code.
      * @param {boolean} isVertexShader - True if the shader is a vertex shader, false if it is a
      * fragment shader.
-     * @returns {WebGLShader} The compiled shader.
+     * @returns {WebGLShader|null} The compiled shader, or null if the device is lost.
      * @private
      */
     _compileShaderSource(device, src, isVertexShader) {
         const gl = device.gl;
 
+        // if the device is lost, silently ignore
+        if (gl.isContextLost()) {
+            return null;
+        }
+
         // device cache for current device, containing cache of compiled shaders
         const shaderDeviceCache = isVertexShader ? _vertexShaderCache : _fragmentShaderCache;
         const shaderCache = shaderDeviceCache.get(device, () => {
@@ -218,11 +223,6 @@ class WebglShader {
 
             glShader = gl.createShader(isVertexShader ? gl.VERTEX_SHADER : gl.FRAGMENT_SHADER);
 
-            // if the device is lost, silently ignore
-            if (!glShader && gl.isContextLost()) {
-                return glShader;
-            }
-
             gl.shaderSource(glShader, src);
             gl.compileShader(glShader);