Bug 720070 - Add missing test for bug 720070. r=needed-tests

js/src/jit-test/tests/basic/bug720070.js

@@ -0,0 +1,6 @@
+var bytes = [0xff, 0xf7, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff]; // big-endian
+bytes.reverse(); // if testing on little-endian
+var result = new Float64Array(new Uint8Array(bytes).buffer)[0];
+
+// Check that this doesn't crash
+isNaN(result + 0);