Fix nans in math::slerp.

libs/math/include/math/TQuatHelpers.h

@@ -250,7 +250,13 @@ public:
         const T a = std::acos(std::abs(d) / npq);
         const T a0 = a * (1 - t);
         const T a1 = a * t;
-        const T isina = 1 / sin(a);
+        const T sina = sin(a);
+        // Prevent blowing up when slerping between two quaternions that are very near each other.
+        static constexpr T value_eps = T(10) * std::numeric_limits<T>::epsilon();
+        if (std::abs(sina) < value_eps) {
+            return lerp(p, q, t);
+        }
+        const T isina = 1 / sina;
         const T s0 = std::sin(a0) * isina;
         const T s1 = std::sin(a1) * isina;
         // ensure we're taking the "short" side