libipa: pwl: Fix single point Pwl

Fix the eval() function for Pwls that contain only a single point.
Remove the should_fail from the corresponding test case.

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/ipa/libipa/pwl.cpp

@@ -210,6 +210,10 @@ double Pwl::eval(double x, int *span, bool updateSpan) const
 					: points_.size() / 2 - 1);
 	if (span && updateSpan)
 		*span = index;
+
+	if (points_.size() == 1)
+		return points_[0].y();
+
 	return points_[index].y() +
 	       (x - points_[index].x()) * (points_[index + 1].y() - points_[index].y()) /
 		       (points_[index + 1].x() - points_[index].x());

test/ipa/libipa/meson.build

@@ -4,7 +4,7 @@ libipa_test = [
     {'name': 'fixedpoint', 'sources': ['fixedpoint.cpp']},
     {'name': 'histogram', 'sources': ['histogram.cpp']},
     {'name': 'interpolator', 'sources': ['interpolator.cpp']},
-    {'name': 'pwl', 'sources': ['pwl.cpp'], 'should_fail': true },
+    {'name': 'pwl', 'sources': ['pwl.cpp'] },
 ]
 
 foreach test : libipa_test