Add guard for IE11 and Edge that don't support lose_context extension.

src/renderers/WebGLRenderer.js

@@ -373,7 +373,11 @@ function WebGLRenderer( parameters ) {
 
 	this.forceContextLoss = function () {
 
-		extensions.get( 'WEBGL_lose_context' ).loseContext();
+		if (extensions.get( 'WEBGL_lose_context' )) {
+
+			extensions.get( 'WEBGL_lose_context' ).loseContext();
+
+		}
 
 	};