Fix an assert in contour_measure.cpp

Since fp32 has finite precision, a segment may reasonably become degenerate with length 0, and we need to be robust enough to handle this. Asserting that the distance is non-negative is still a good test.

Fixes #7210.

Diffs=
806ae1fae Fix an assert in contour_measure.cpp (#7232)

Co-authored-by: Chris Dalton <99840794+csmartdalton@users.noreply.github.com>

.rive_head

@@ -1 +1 @@
-7d03c3fafeefd05513c4a418f320322ecd1c1e4e
+806ae1faea4cc10452c76a4ce2b35f2ca12aa469

src/math/contour_measure.cpp

@@ -34,7 +34,7 @@ ContourMeasure::ContourMeasure(std::vector<Segment>&& segs,
 // or the last segment if distance == m_distance
 size_t ContourMeasure::findSegment(float distance) const
 {
-    assert(m_segments.front().m_distance > 0);
+    assert(m_segments.front().m_distance >= 0);
     assert(m_segments.back().m_distance == m_length);
 
     assert(distance >= 0 && distance <= m_length);