Handle NULL coverage table in ligature substitute
Just to be in line with Single and Alternate subst.
diff --git a/Lib/fontTools/ttLib/tables/otTables.py b/Lib/fontTools/ttLib/tables/otTables.py
index 481b0b0..7005c71 100644
--- a/Lib/fontTools/ttLib/tables/otTables.py
+++ b/Lib/fontTools/ttLib/tables/otTables.py
@@ -400,7 +400,7 @@
def postRead(self, rawTable, font):
ligatures = {}
if self.Format == 1:
- input = rawTable["Coverage"].glyphs
+ input = _getGlyphsFromCoverageTable(rawTable["Coverage"])
ligSets = rawTable["LigatureSet"]
assert len(input) == len(ligSets)
for i in range(len(input)):