Fix git-p4 decode() missing an assignment

bugfix: When using git-p4 in the python2 environment, some places decode() missing an assignment.

Signed-off-by: SaNeOr <sane0r@outlook.com>

git-p4.py

@@ -258,7 +258,7 @@ def metadata_stream_to_writable_bytes(s):
     if encodingStrategy == 'passthrough':
         return s
     try:
-        s.decode('utf_8')
+        s = s.decode('utf_8')
         return s
     except UnicodeDecodeError:
         if encodingStrategy == 'fallback' and fallbackEncoding:
@@ -307,7 +307,7 @@ def decode_path(path):
         return path.decode(encoding, errors='replace') if isinstance(path, bytes) else path
     else:
         try:
-            path.decode('ascii')
+            path = path.decode('ascii')
         except:
             path = path.decode(encoding, errors='replace')
             if verbose:
@@ -3114,7 +3114,7 @@ def writeToGitStream(self, gitMode, relPath, contents):
 
     def encodeWithUTF8(self, path):
         try:
-            path.decode('ascii')
+            path = path.decode('ascii')
         except:
             encoding = 'utf8'
             if gitConfig('git-p4.pathEncoding'):