Support wrapping functions not returning promises.

src/Task.ts

@@ -32,7 +32,7 @@ export function tryFinally<PromiseType extends Promisy<PromiseType>>(
 		promise = func();
 
 		// Ensure func return value is a promise.
-		if(typeof(promise.then) != 'function') {
+		if(typeof(promise) != 'object' || typeof(promise.then) != 'function') {
 			promise = Promise.resolve(promise);
 		}
 	} catch(err) {

src/TaskQueue.ts

@@ -21,7 +21,7 @@ export class TaskQueue<PromiseType extends Promisy<PromiseType>> {
 	  * @param func Function to call.
 	  * @param delay Initial delay in milliseconds before making the call. */
 
-	add(func: () => PromiseType, delay = 0) {
+	add(func: () => any, delay = 0) {
 		if(this.busyCount < this.concurrency && !delay) {
 			// Start the task immediately.
 
@@ -57,7 +57,7 @@ export class TaskQueue<PromiseType extends Promisy<PromiseType>> {
 	/** Wrap a function returning a promise, so that before running
 	  * it waits until concurrent invocations are below this queue's limit. */
 
-	wrap(func: (...args: any[]) => PromiseType, thisObject?: any) {
+	wrap(func: (...args: any[]) => any, thisObject?: any) {
 		return((...args: any[]) => this.add(() => func.apply(thisObject, args)));
 	}