Check whether context is lost before gl.shaderSource(...).

When context is lost most gl calls are no-ops but this one can throw.
When a program cannot be created `draw(...)` needs to fail silently just
like all gl calls.

fix #8986

src/render/program.js

@@ -27,6 +27,7 @@ class Program<Us: UniformBindings> {
     numAttributes: number;
     fixedUniforms: Us;
     binderUniforms: Array<BinderUniform>;
+    failedToCreate: boolean;
 
     constructor(context: Context,
                 source: {fragmentSource: string, vertexSource: string},
@@ -44,12 +45,14 @@ class Program<Us: UniformBindings> {
         const fragmentSource = defines.concat(prelude.fragmentSource, source.fragmentSource).join('\n');
         const vertexSource = defines.concat(prelude.vertexSource, source.vertexSource).join('\n');
         const fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
+        if (this.failedToCreate = gl.isContextLost()) return;
         gl.shaderSource(fragmentShader, fragmentSource);
         gl.compileShader(fragmentShader);
         assert(gl.getShaderParameter(fragmentShader, gl.COMPILE_STATUS), (gl.getShaderInfoLog(fragmentShader): any));
         gl.attachShader(this.program, fragmentShader);
 
         const vertexShader = gl.createShader(gl.VERTEX_SHADER);
+        if (this.failedToCreate = gl.isContextLost()) return;
         gl.shaderSource(vertexShader, vertexSource);
         gl.compileShader(vertexShader);
         assert(gl.getShaderParameter(vertexShader, gl.COMPILE_STATUS), (gl.getShaderInfoLog(vertexShader): any));
@@ -110,6 +113,8 @@ class Program<Us: UniformBindings> {
 
         const gl = context.gl;
 
+        if (this.failedToCreate) return;
+
         context.program.set(this.program);
         context.setDepthMode(depthMode);
         context.setStencilMode(stencilMode);