Bug 973574 - Fix AutoDebugModeInvalidation to not call FinishDiscardJitCode if it didn't discard JIT code. r=shu

js/src/jit/Ion.cpp

@@ -2879,7 +2879,9 @@ AutoDebugModeInvalidation::~AutoDebugModeInvalidation()
     if (comp_) {
         FinishDiscardJitCode(fop, comp_);
     } else {
-        for (CompartmentsInZoneIter comp(zone_); !comp.done(); comp.next())
-            FinishDiscardJitCode(fop, comp);
+        for (CompartmentsInZoneIter comp(zone_); !comp.done(); comp.next()) {
+            if (comp->principals)
+                FinishDiscardJitCode(fop, comp);
+        }
     }
 }