Fix multiple error bug

This commit fixes a bug where the done callback may be called more
than once.

Author: kgryte

lib/node_modules/@stdlib/utils/count-by-async/lib/limit.js

@@ -85,14 +85,14 @@ function limit( collection, opts, indicator, done ) {
 		* @returns {void}
 		*/
 		function cb( error, group ) {
-			if ( error ) {
-				flg = true;
-				return clbk( error );
-			}
 			if ( flg ) {
 				// Prevent further processing of collection elements:
 				return;
 			}
+			if ( error ) {
+				flg = true;
+				return clbk( error );
+			}
 			debug( 'Collection element %d group: %s.', j, group );
 
 			// Checking for an "own" property is necessary to guard against the edge case where an indicator function returns a group identifier which matches a method or property on the `Object` prototype.

lib/node_modules/@stdlib/utils/count-by-async/test/test.count_by.js

@@ -845,6 +845,34 @@ tape( 'if an error is encountered while processing a collection element, the fun
 	}
 });
 
+tape( 'if an error is encountered while processing a collection element, the function suspends execution and immediately returns the error (concurrent)', function test( t ) {
+	var count;
+	var arr;
+
+	arr = [ 500, 500, 500 ];
+	count = 0;
+	countByAsync( arr, indicator, done );
+
+	function indicator( value, index, next ) {
+		count += 1;
+		setTimeout( onTimeout, value );
+
+		function onTimeout() {
+			return next( new Error( 'beep' ) );
+		}
+	}
+
+	function done( error ) {
+		t.strictEqual( count, 3, 'suspends execution' );
+		if ( error ) {
+			t.pass( error.message );
+		} else {
+			t.fail( 'did not return an error' );
+		}
+		t.end();
+	}
+});
+
 tape( 'if provided an empty collection, the function never invokes an indicator function and returns an empty object', function test( t ) {
 	var arr = [];
 	countByAsync( arr, indicator, done );

lib/node_modules/@stdlib/utils/count-by-async/test/test.factory.js

@@ -958,6 +958,37 @@ tape( 'if an error is encountered while processing a collection element, the ret
 	}
 });
 
+tape( 'if an error is encountered while processing a collection element, the returned function suspends execution and immediately returns the error (concurrent)', function test( t ) {
+	var countByAsync;
+	var count;
+	var arr;
+
+	countByAsync = factory( indicator );
+
+	arr = [ 500, 500, 500 ];
+	count = 0;
+	countByAsync( arr, done );
+
+	function indicator( value, index, next ) {
+		count += 1;
+		setTimeout( onTimeout, value );
+
+		function onTimeout() {
+			return next( new Error( 'beep' ) );
+		}
+	}
+
+	function done( error ) {
+		t.strictEqual( count, 3, 'suspends execution' );
+		if ( error ) {
+			t.pass( error.message );
+		} else {
+			t.fail( 'did not return an error' );
+		}
+		t.end();
+	}
+});
+
 tape( 'if provided an empty collection, the returned function never invokes an indicator function and returns an empty object', function test( t ) {
 	var countByAsync;
 	var arr;