fix tnetstread crash found via fuzzing

mitmproxy/io/io.py

@@ -46,7 +46,7 @@ class FlowReader:
                 if mdata["type"] not in FLOW_TYPES:
                     raise exceptions.FlowReadException("Unknown flow type: {}".format(mdata["type"]))
                 yield FLOW_TYPES[mdata["type"]].from_state(mdata)
-        except (ValueError, TypeError) as e:
+        except (ValueError, TypeError, IndexError) as e:
             if str(e) == "not a tnetstring: empty file":
                 return  # Error is due to EOF
             raise exceptions.FlowReadException("Invalid data format.")

test/mitmproxy/io/test_io.py

@@ -11,6 +11,7 @@ from mitmproxy.io import FlowReader, tnetstring
 class TestFlowReader:
     @given(binary())
     @example(b'51:11:12345678901#4:this,8:true!0:~,4:true!0:]4:\\x00,~}')
+    @example(b'0:')
     def test_fuzz(self, data):
         f = io.BytesIO(data)
         reader = FlowReader(f)