Fix #538: PDFValidation for PDF/A-3A always invalid

This fixes the bug where validation of actually valid PDF/A-3A files
always claimed that the PDF is "Not a PDF/A-3".
In fact, the validation was only accepting levels 3B and 3U.

validator/src/test/java/org/mustangproject/validator/ZUGFeRDValidatorTest.java

@@ -141,6 +141,17 @@ public class ZUGFeRDValidatorTest extends ResourceCase {
 
   }
 
+	public void testPDFA3AValidation() {
+		File tempFile = getResourceAsFile("zugferd_2p1_EXTENDED_PDFA-3A.pdf");
+
+		ZUGFeRDValidator zfv = new ZUGFeRDValidator();
+
+		String res = zfv.validate(tempFile.getAbsolutePath());
+
+		assertThat(res).valueByXPath("/validation/pdf/summary/@status")
+			.isEqualTo("valid");
+	}
+
 	/***
 	 * the XMLValidatorTests only cover the <xml></xml> part, this one includes the root element and
 	 * the global <summary></summary> part as well