Make Range return 1.0 ratio if minimum and maximum values are equal

An error message is also no longer printed.
This matches the behavior found in most UI frameworks where having
equal minimum and maximum values is considered acceptable.

This closes #43179.

scene/gui/range.cpp

@@ -171,7 +171,10 @@ void Range::set_as_ratio(double p_value) {
 }
 
 double Range::get_as_ratio() const {
-	ERR_FAIL_COND_V_MSG(Math::is_equal_approx(get_max(), get_min()), 0.0, "Cannot get ratio when minimum and maximum value are equal.");
+	if (Math::is_equal_approx(get_max(), get_min())) {
+		// Avoid division by zero.
+		return 1.0;
+	}
 
 	if (shared->exp_ratio && get_min() >= 0) {
 		double exp_min = get_min() == 0 ? 0.0 : Math::log(get_min()) / Math::log((double)2);