The variant of `RNA_property_string_get()` that returns a `std::string`
always returned a string with zero length. The issue is that it was only
calling `reserve()`, which ensures an underlying buffer with enough
*capacity*, but does not set the string length. The property's string
value would then be correctly copied to the reserved buffer, but the
string length would remain zero.
This commit fixes the issue by replacing the call to `reserve()` with a
call to `resize()`, which additionally sets the string length.
Pull Request: https://projects.blender.org/blender/blender/pulls/139106
984a2b5298