convert: migrate to util.iterfile

hgext/convert/common.py

@@ -454,7 +454,7 b' class mapfile(dict):'
             if err.errno != errno.ENOENT:
                 raise
             return
-        for i, line in enumerate(fp):
+        for i, line in enumerate(util.iterfile(fp)):
             line = line.splitlines()[0].rstrip()
             if not line:
                 # Ignore blank lines

hgext/convert/convcmd.py

@@ -201,7 +201,7 b' class converter(object):'
         m = {}
         try:
             fp = open(path, 'r')
-            for i, line in enumerate(fp):
+            for i, line in enumerate(util.iterfile(fp)):
                 line = line.splitlines()[0].rstrip()
                 if not line:
                     # Ignore blank lines