Let the annotation indexer ignore .jar files that have gone AWOL

This happens for example when the ImageJ2 updater removes obsolete
versions, therefore we have to handle that situation gracefully.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

src/main/java/org/scijava/annotations/Index.java

@@ -142,7 +142,12 @@ public IndexItemIterator(final Class<A> annotation) {
 		private void readNext() throws IOException {
 			for (;;) {
 				if (indexReader == null) {
-					indexReader = getNextReader();
+					try {
+						indexReader = getNextReader();
+					} catch (IOException e) {
+						e.printStackTrace();
+						continue;
+					}
 					if (indexReader == null) {
 						urls = null;
 						next = null;