AP_Math: judge isnan judgment before operation

libraries/AP_Math/vector2.cpp

@@ -199,15 +199,21 @@ bool Vector2<T>::circle_segment_intersection(const Vector2<T>& seg_start, const
     const float a = sq(seg_end_minus_start.x) + sq(seg_end_minus_start.y);
     const float b = 2 * ((seg_end_minus_start.x * seg_start_local.x) + (seg_end_minus_start.y * seg_start_local.y));
     const float c = sq(seg_start_local.x) + sq(seg_start_local.y) - sq(radius);
+
+    if (isnan(a) || isnan(b) || isnan(c)) {
+       return false;
+    }
+
     const float delta = sq(b) - (4.0f * a * c);
 
+    if (isnan(delta)) {
+       return false;
+    }
+
     // check for invalid data
     if (::is_zero(a)) {
         return false;
     }
-    if (isnan(a) || isnan(b) || isnan(c) || isnan(delta)) {
-       return false;
-    }
 
     // check for invalid delta (i.e. discriminant)
     if (delta < 0.0f) {