JS: fix false positives for splice with conditional index decrement

javascript/ql/src/Statements/LoopIterationSkippedDueToShifting.ql

@@ -146,7 +146,12 @@ class ArrayIterationLoop extends ForStmt {
     or
     this.hasPathThrough(splice, cfg.getAPredecessor()) and
     this.getLoopEntry().dominates(cfg.getBasicBlock()) and
-    not this.hasIndexingManipulation(cfg)
+    not this.hasIndexingManipulation(cfg) and
+    // Don't continue through a branch that tests the splice call's return value
+    not exists(ConditionGuardNode guard | cfg = guard |
+      guard.getTest() = splice.asExpr() and
+      guard.getOutcome() = false
+    )
   }
 }