libcamera: yaml_parser: Improve efficiency of string empty check

Comparing a std::string to an empty string literal is more complex than
using the std::string::empty() function. Improve the code efficiency by
replacing the former with the latter.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/yaml_parser.cpp

@@ -194,7 +194,7 @@ YamlObject::Getter<double>::get(const YamlObject &obj) const
 	if (obj.type_ != Type::Value)
 		return std::nullopt;
 
-	if (obj.value_ == "")
+	if (obj.value_.empty())
 		return std::nullopt;
 
 	char *end;