Avoid using non-disposed resources in LabelTest

This corrects a minor oversight introduced with
2e46a0b. One of the tests creates a new
Font, but never disposes it, even though an identical Font is created
that is disposed once the test finishes.

Author: ptziegler

org.eclipse.draw2d.tests/src/org/eclipse/draw2d/test/LabelTest.java

@@ -135,7 +135,7 @@ public void test_getPreferredSize() throws Exception {
 		assertSame(size2, label.getPreferredSize());
 		//
 		// check calc preferred size if font is changed
-		label.setFont(new Font(null, "", 100, SWT.NONE)); //$NON-NLS-1$
+		label.setFont(testFont);
 		assertNotSame(size2, label.getPreferredSize());
 		assertTextSize(label);
 		//