Use the new strings_to_ctypes_array function

pygmt/clib/session.py

@@ -641,11 +641,8 @@ def call_module(self, module: str, args: list[str]):
             # This is the preferred way to pass arguments to GMT API, because we don't
             # have to deal with whitespaces or quotation marks on the PyGMT side.
             mode = len(args)  # Now mode is the number of arguments.
-            if mode == 0:  # No arguments, passing a null pointer
-                argv = None
-            else:
-                argv = (ctp.c_char_p * len(args))()
-                argv[:] = np.char.encode(args)
+            # Pass a null pointer if no arguments are specified.
+            argv = strings_to_ctypes_array(args) if mode != 0 else None
         else:
             raise GMTInvalidInput(
                 "'args' must be either a string or a list of strings."