[lldb] Unconditionally strip the `.py(c)` extension as we always import Python modules

[JDevlieghere]

Summary

Currently we only strip the Python extension when the file exists on disk because we assumed that if it didn't exist it was a module. However, with the change from D89334 this is no longer the case as we want to be able to import a relative path to a .py as a module. Since we always import a scripting module as a "python module" we should always strip the extension if present.

This is necessary to write a test with a .py extension as suggested by Dave:

In D89334#2328372, @kastiglione wrote:

Would you mind adding a couple tests for imports via a path to a python file, ex command script import command.py, maybe even a test that checks nested directories, ex: command script import path/to/command.py?

lldb/source/Plugins/ScriptInterpreter/Python/ScriptInterpreterPython.cpp

                                    .SetEnableIO(false)
                                    .SetSetLLDBGlobals(false))
               .Success();
       if (!syspath_retval) {
         error.SetErrorString("Python sys.path handling failed");
         return false;
       }
 
-      // strip .py or .pyc extension
-      ConstString extension = target_file.GetFileNameExtension();
-      if (extension) {
-        if (llvm::StringRef(extension.GetCString()) == ".py")
-          basename.resize(basename.length() - 3);
-        else if (llvm::StringRef(extension.GetCString()) == ".pyc")
-          basename.resize(basename.length() - 4);
-      }
     } else {
       error.SetErrorString("no known way to import this module specification");
       return false;
     }
 
+    // Strip .py or .pyc extension
+    llvm::StringRef extension = target_file.GetFileNameExtension().GetCString();
+    if (!extension.empty()) {
+      if (extension == ".py")
+        basename.resize(basename.length() - 3);
+      else if (extension == ".pyc")
+        basename.resize(basename.length() - 4);
+    }
+
     // check if the module is already import-ed
     command_stream.Clear();
     command_stream.Printf("sys.modules.__contains__('%s')", basename.c_str());
     bool does_contain = false;
     // this call will succeed if the module was ever imported in any Debugger
     // in the lifetime of the process in which this LLDB framework is living
     bool was_imported_globally =
         (ExecuteOneLineWithReturn(