[File Connector][Delete]No valid message is provided when there are no files existing of the specified file type to delete

[isuruuy429]

Steps to reproduce:

1. Create the following API in the WSO2 Integration Studio.

<?xml version="1.0" encoding="UTF-8"?>
<api context="/connect" name="Connect" xmlns="http://ws.apache.org/ns/synapse">
<resource methods="POST" uri-template="/delete">
        <inSequence>
            <property expression="json-eval($.source)" name="source" scope="default" type="STRING"/>
            <property expression="json-eval($.filePattern)" name="filePattern" scope="default" type="STRING"/>
            <fileconnector.delete>
                <source>{$ctx:source}</source>
                <filePattern>{$ctx:filePattern}</filePattern>
            </fileconnector.delete>
            <respond/>
        </inSequence>
        <outSequence/>
        <faultSequence/>
    </resource>
</api>

2. Invoke the API by specifying a folder where it does not exist the specified types of files in the filePattern in the payload.
   eg: If my payload is as below, in the 'new` folder, do not include any JSON file.

{
	"source":"/Users/IsuruUyanage/Desktop/RnD/2020/Q1/ConnectorVerification/wso2-extentions/docs3/FileConnectorTesting/test/read/new",
	"filePattern":".*.json"
}

Expected: It should provide an error message saying that the specified type of file does not exist and return false.
Actual: It returns true and no error message provided.