Fix PYTHONIOENCODING parsing when encoding is empty + address review comments

Author: steve-s

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/GraalPythonModuleBuiltins.java

@@ -129,14 +129,14 @@ public void initialize(PythonCore core) {
         String standardStreamError;
         if (encodingOpt != null && !encodingOpt.isEmpty()) {
             String[] parts = encodingOpt.split(":");
-            standardStreamEncoding = parts[0];
-            standardStreamError = parts.length > 1 ? parts[1] : "strict";
+            standardStreamEncoding = parts[0].isEmpty() ? "utf-8" : parts[0];
+            standardStreamError = parts.length > 1 && !parts[1].isEmpty() ? parts[1] : "strict";
         } else {
             standardStreamEncoding = "utf-8";
             standardStreamError = "surrogateescape";
         }
 
-        if (LOGGER.isLoggable(Level.INFO)) {
+        if (LOGGER.isLoggable(Level.FINE)) {
             LOGGER.fine(String.format("Setting default stdio encoding to %s:%s", standardStreamEncoding, standardStreamError));
         }
         this.builtinConstants.put("stdio_encoding", standardStreamEncoding);

graalpython/lib-graalpython/pyio_patches.py

@@ -83,7 +83,6 @@ def open(*args, **kwargs):
 
 setattr(builtins, 'open', open)
 
-import __graalpython__
 sys.stdin = _pyio.TextIOWrapper(_pyio.BufferedReader(sys.stdin), encoding=__graalpython__.stdio_encoding, errors=__graalpython__.stdio_error, line_buffering=True)
 sys.stdin.mode = "r"
 sys.__stdin__ = sys.stdin