fix: change ArcCircleInstruction radius from Point to Unit; assertion for safety

tinyvg.odin

@@ -127,7 +127,7 @@ CubicBezierInstruction :: struct {
 ArcCircleInstruction :: struct {
     large_arc: bool,
     sweep: bool,
-    radius: Point,
+    radius: Unit,
     target: Point,
 }
 ArcEllipseInstruction :: struct {
@@ -581,6 +581,7 @@ read_unit :: proc(r: ^Reader, header: Header) -> (unit: f32, err: Error) {
 
 @(private, require_results)
 read_path :: proc(r: ^Reader, header: Header, segment_count: u32) -> (path: Path, err: Error) {
+    assert(segment_count <= 1024) // arbitrary limit to avoid unbounded allocations on malformed input
     segments_instructions: [1024]u32
     segments := make([]Segment, segment_count)