Fix potential UB when target_file directory is null

[sgraenitz]

Summary

As seen in a crash report, the C-string returned for the directory component of target_file can null. It should not be assigned to std::string directly as this is undefined behavior.

[sgraenitz]

Remove useless newline

[jingham]

Might be clearer to do:

if (target_file.GetDirectory().IsEmpty()) {
    error...
}
std::string directory = ...

Avoids the extra variable and also adds the check for "", which I don't think we want to add to sys.path either.

[sgraenitz]

Polish && error out also on empty string

[sgraenitz]

Ping

[jingham]

That code seems amazingly good to me ;-)

source/Plugins/ScriptInterpreter/Python/ScriptInterpreterPython.cpp

if (ec || st.type() == fs::file_type::status_error ||
       // dot can't be used but / and \ can, and if either is found, reject
       if (strchr(pathname, '\\') || strchr(pathname, '/')) {
         error.SetErrorString("invalid pathname");
         return false;
       }
       basename = pathname; // not a filename, probably a package of some sort,
                            // let it go through
     } else if (is_directory(st) || is_regular_file(st)) {
+      if (target_file.GetDirectory().IsEmpty()) {
+        error.SetErrorString("invalid directory name");
+        return false;
+      }
+
       std::string directory = target_file.GetDirectory().GetCString();
       replace_all(directory, "\\", "\\\\");
       replace_all(directory, "'", "\\'");
 
       // now make sure that Python has "directory" in the search path
       StreamString command_stream;
       command_stream.Printf("if not (sys.path.__contains__('%s')):\n    "
                             "sys.path.insert(1,'%s');\n\n",