[Memory64] pthread JS changes for 64-bit

Author: aardappel

src/library_pthread.js

@@ -666,7 +666,7 @@ var LibraryPThread = {
     // Deduce which WebGL canvases (HTMLCanvasElements or OffscreenCanvases) should be passed over to the
     // Worker that hosts the spawned pthread.
     // Comma-delimited list of CSS selectors that must identify canvases by IDs: "#canvas1, #canvas2, ..."
-    var transferredCanvasNames = attr ? {{{ makeGetValue('attr', 36, 'i32') }}} : 0;
+    var transferredCanvasNames = attr ? {{{ makeGetValue('attr', 40, POINTER_TYPE) }}} : 0;
 #if OFFSCREENCANVASES_TO_PTHREAD
     // Proxied canvases string pointer -1 is used as a special token to fetch
     // whatever canvases were passed to build in -s