GLTFExporter: handle count=Infinity in processAccessor (#26898)

Co-authored-by: Mr David <[email protected]>

examples/jsm/exporters/GLTFExporter.js

@@ -1165,7 +1165,7 @@ class GLTFWriter {
 		}
 
 		if ( start === undefined ) start = 0;
-		if ( count === undefined ) count = attribute.count;
+		if ( count === undefined || count === Infinity ) count = attribute.count;
 
 		// Skip creating an accessor if the attribute doesn't have data to export
 		if ( count === 0 ) return null;