Bug 838955 (part 1) - Fix rooting hazards in jsstr.cpp identified by static analysis. r=sfink.

--HG--
extra : rebase_source : cc45015a1840ccb1c3146e0b4ad81f2226dac985

js/src/jsstr.cpp

@@ -2043,7 +2043,8 @@ FindReplaceLength(JSContext *cx, RegExpStatics *res, ReplaceData &rdata, size_t
         rdata.elembase = NULL;
     }
 
-    if (JSObject *lambda = rdata.lambda) {
+    if (rdata.lambda) {
+        RootedObject lambda(cx, rdata.lambda);
         PreserveRegExpStatics staticsGuard(cx, res);
         if (!staticsGuard.init(cx))
             return false;