xmltok: Change StopIteration to EOFError due to PEP-479.

Due to changes in MicroPython to support PEP-479, StopIteration has been
deprecated for return.  This results in xmltok to raise RuntimeError every
time.  This commit is a simple fix to just change from StopIteration to
EOFError and then return it in the generator.

micropython/xmltok/xmltok.py

@@ -31,7 +31,7 @@ class XMLTokenizer:
     def nextch(self):
         self.c = self.f.read(1)
         if not self.c:
-            raise StopIteration
+            raise EOFError
         return self.c
 
     def skip_ws(self):
@@ -87,6 +87,7 @@ class XMLTokenizer:
 
     def tokenize(self):
         while not self.eof():
+            try:
                 if self.match("<"):
                     if self.match("/"):
                         yield (END_TAG, self.getnsident())
@@ -117,6 +118,8 @@ class XMLTokenizer:
                         text += self.getch()
                     if text:
                         yield (TEXT, text)
+            except EOFError:
+                pass
 
 
 def gfind(gen, pred):