Use StreamUtil in CertificateManager

Change-Id: I01438bd22213fadffee63cd131efffbf1a77da18
Reviewed-on: http://gerrit.dmdirc.com/545
Automatic-Compile: Gregory Holmes <greboid@dmdirc.com>
Reviewed-by: Gregory Holmes <greboid@dmdirc.com>

src/com/dmdirc/CertificateManager.java

 import com.dmdirc.logger.Logger;
 import com.dmdirc.ui.core.dialogs.sslcertificate.CertificateAction;
 import com.dmdirc.ui.core.dialogs.sslcertificate.SSLCertificateDialogModel;
+import com.dmdirc.util.StreamUtil;
 
 import java.io.File;
 import java.io.FileInputStream;
 import javax.net.ssl.KeyManager;
 import javax.net.ssl.KeyManagerFactory;
 import javax.net.ssl.X509TrustManager;
+
 import net.miginfocom.Base64;
 
 /**
             } catch (UnrecoverableKeyException ex) {
                 Logger.appError(ErrorLevel.MEDIUM, "Unable to get key manager", ex);
             } finally {
-                if (fis != null) {
-                    try {
-                        fis.close();
-                    } catch (IOException ex) {
-                        // ...
-                    }
-                }
+                StreamUtil.close(fis);
             }
         }