Skip empty files in G3Reader

Avoid throwing an IO error when an empty G3 file is included in the input
filenames by silently moving on to the next file in the list until reaching a
non-empty file or the end of the list.

Fixes #134.

core/src/G3Reader.cxx

@@ -80,7 +80,7 @@ void G3Reader::Process(G3FramePtr frame, std::deque<G3FramePtr> &out)
 	if (Py_IsInitialized())
 		_save = PyEval_SaveThread();
 
-	if (stream_.peek() == EOF) {
+	while (stream_.peek() == EOF) {
 		if (filename_.size() > 0) {
 			StartFile(filename_.front());
 			filename_.pop_front();

core/tests/fileio.py

@@ -46,7 +46,16 @@ def checkinfo(fr):
     n += 1
 pipe.Add(checkinfo)
 pipe.Run()
+assert n == 10, 'Wrong number of frames read (%d should be %d)' % (n, 10)
 
+# Skip empty files
+wr = core.G3Writer("empty.g3")
+del wr
+n = 0
+pipe = core.G3Pipeline()
+pipe.Add(core.G3Reader, filename=["empty.g3", "test.g3", "empty.g3"], track_filename=True)
+pipe.Add(checkinfo)
+pipe.Run()
 assert n == 10, 'Wrong number of frames read (%d should be %d)' % (n, 10)
 
 # Indexing