Fixed plistlib API usage

plistlib API required the file object opened in the binary mode.
Test command: lnt checkformat tests/SharedInputs/sample-a-small.plist
Related to: https://reviews.llvm.org/D109235

Reviewed By: thopre

Differential Revision: https://reviews.llvm.org/D112136

Huawei Russian Research Institute, Saint-Petersburg

Author: Pavel Kosov

lnt/formats/PlistFormat.py

@@ -3,15 +3,27 @@
 
 def _matches_format(path_or_file):
     try:
-        plistlib.load(path_or_file)
+        if isinstance(path_or_file, str):
+            with open(path_or_file, 'rb') as fp:
+                plistlib.load(fp)
+        else:
+            plistlib.load(path_or_file)
         return True
     except Exception:
         return False
 
 
+def _load_format(path_or_file):
+    if isinstance(path_or_file, str):
+        with open(path_or_file, 'rb') as fp:
+            return plistlib.load(fp)
+    else:
+        return plistlib.load(path_or_file)
+
+
 format = {
     'name': 'plist',
     'predicate': _matches_format,
-    'read': plistlib.load,
+    'read': _load_format,
     'write': plistlib.dump,
 }