[ttLib.tables._n_a_m_e] Fix #1997: Only attempt to recovered malforme…

…d data from bytes (#1998)

* don't attempt to recover malformed data from str, only from bytes. Fixes #1997

Lib/fontTools/ttLib/tables/_n_a_m_e.py

@@ -441,7 +441,7 @@ def isascii(b):
 		encoding = self.getEncoding()
 		string = self.string
 
-		if encoding == 'utf_16_be' and len(string) % 2 == 1:
+		if isinstance(string, bytes) and encoding == 'utf_16_be' and len(string) % 2 == 1:
 			# Recover badly encoded UTF-16 strings that have an odd number of bytes:
 			# - If the last byte is zero, drop it.  Otherwise,
 			# - If all the odd bytes are zero and all the even bytes are ASCII,

Tests/ttLib/tables/_n_a_m_e_test.py

@@ -345,6 +345,11 @@ def test_toUnicode_UnicodeDecodeError(self):
 		self.assertEqual("utf_16_be", name.getEncoding())
 		self.assertRaises(UnicodeDecodeError, name.toUnicode)
 
+	def test_toUnicode_singleChar(self):
+		# https://github.com/fonttools/fonttools/issues/1997
+		name = makeName("A", 256, 3, 1, 0x409)
+		self.assertEqual(name.toUnicode(), "A")
+
 	def toXML(self, name):
 		writer = XMLWriter(BytesIO())
 		name.toXML(writer, ttFont=None)