LibJS: Use assertNotReached() in tests

Author: https://github.com/linusg
Commit: b9415dc0e9
Pull-request: https://github.com/SerenityOS/serenity/pull/1782

Libraries/LibJS/Tests/throw-basic.js

@@ -1,11 +1,13 @@
 try {
     throw 1;
+    assertNotReached();
 } catch (e) {
     assert(e === 1);
 }
 
 try {
     throw [99];
+    assertNotReached();
 } catch (e) {
     assert(typeof e === "object");
     assert(e.length === 1);
@@ -13,10 +15,12 @@ try {
 
 function foo() {
     throw "hello";
+    assertNotReached();
 }
 
 try {
     foo();
+    assertNotReached();
 } catch (e) {
     assert(e === "hello");
 }