fix libsodium.so.23 cannot find on some strange linux environment

that case by ```ctypes.util.find_library()``` have different find path from ```CDLL()```

shadowsocks/crypto/util.py

@@ -68,7 +68,9 @@ def find_library(possible_lib_names, search_symbol, library_name):
             if path:
                 paths.append(path)
 
-    if not paths:
+    # always find lib on extend path that to avoid ```CDLL()``` failed on some strange linux environment
+    # in that case ```ctypes.util.find_library()``` have different find path from ```CDLL()```
+    if True:
         # We may get here when find_library fails because, for example,
         # the user does not have sufficient privileges to access those
         # tools underlying find_library on linux.