TOOLS/matroska.py: stop cleanly at EOF of complete file when parsing

When using the script to parse a Matroska file, the script used to
exit with an exception at EOF. Change it to exit quietly instead if
the file was parsed successfully. Keep showing an exception if EOF is
encountered in the middle of an element (truncated file).

TOOLS/matroska.py

@@ -183,6 +183,8 @@ from binascii import hexlify
 def byte2num(s):
     return int(hexlify(s), 16)
 
+class EOF(Exception): pass
+
 def camelcase_to_words(name):
     parts = []
     start = 0
@@ -295,7 +297,7 @@ def generate_C_definitions():
 def read(s, length):
     t = s.read(length)
     if len(t) != length:
-        raise IOError
+        raise EOF
     return t
 
 def read_id(s):
@@ -411,4 +413,10 @@ elif sys.argv[1] == '--generate-definitions':
 else:
     s = open(sys.argv[1], "rb")
     while 1:
-        parse_toplevel(s)
+        start = s.tell()
+        try:
+            parse_toplevel(s)
+        except EOF:
+            if s.tell() != start:
+                raise Exception("Unexpected end of file")
+            break