Merge pull request #600 from Malte-Neu/fixResourceHandle

Fixes a problem where a stream was not safely closed

library/src/main/java/org/mustangproject/ZUGFeRD/ZUGFeRDExporterFromPDFA.java

@@ -83,8 +83,9 @@ public class ZUGFeRDExporterFromPDFA implements IZUGFeRDExporter {
 	}
 
 	protected byte[] filenameToByteArray(String pdfFilename) throws IOException {
-		FileInputStream fileInputStream = new FileInputStream(pdfFilename);
-		return inputstreamToByteArray(fileInputStream);
+		try (FileInputStream fileInputStream = new FileInputStream(pdfFilename)) {
+			return inputstreamToByteArray(fileInputStream);
+		}
 	}
 
 	protected byte[] inputstreamToByteArray(InputStream fileInputStream) throws IOException  {