Minor adjustments to Android port

* java/org/gnu/emacs/EmacsService.java (readDirectoryEntry):
Also refrain from returning NULL or file names containing
non-representable NULL bytes.
* src/callproc.c (get_current_directory): Clean up by employing
android_is_special_directory.

java/org/gnu/emacs/EmacsService.java

@@ -1503,9 +1503,13 @@ public final class EmacsService extends Service
 	    return entry;
 	  }
 
-	/* Skip this entry if its name cannot be represented.  */
+	/* Skip this entry if its name cannot be represented.  NAME
+	   can still be null here, since some Cursors are permitted to
+	   return NULL if INDEX is not a string.  */
 
-	if (name.equals ("..") || name.equals (".") || name.contains ("/"))
+	if (name == null || name.equals ("..")
+	    || name.equals (".") || name.contains ("/")
+	    || name.contains ("\0"))
 	  continue;
 
 	/* Now, look for its type.  */