renderer: fixed a memory leak

This issue only valid on the main branch.

regression by 1806b32971

issue: https://github.com/thorvg/thorvg/issues/3070

src/renderer/tvgPaint.h

@@ -109,7 +109,7 @@ namespace tvg
 
             if (free && refCnt == 0) {
                 //TODO: use the global dismiss function?
-                delete(this);
+                delete(paint);
                 return 0;
             }