[cairo-arc] Check that the context is not error before proceeding.

We depend on values stored on the context that become invalid upon an
error, so stop processing as soon as an error occurs. Prior to
adjusting, the values returned from the error context, this would cause
an infinite loop whilst calculating the number of segments required for
a tolerance of 0.

src/cairo-arc.c

@@ -181,6 +181,9 @@ _cairo_arc_in_direction (cairo_t	  *cr,
 			 double		   angle_max,
 			 cairo_direction_t dir)
 {
+    if (cairo_status (cr))
+        return;
+
     while (angle_max - angle_min > 4 * M_PI)
 	angle_max -= 2 * M_PI;