Bug 583200 - Don't assert things about SHEntries if session history is disabled.

docshell/base/nsDocShell.cpp

@@ -9045,7 +9045,7 @@ nsDocShell::OnNewURI(nsIURI * aURI, nsIChannel * aChannel, nsISupports* aOwner,
            ("  shAvailable=%i updateHistory=%i equalURI=%i\n",
             shAvailable, updateHistory, equalUri));
 
-    if (mCurrentURI && !mOSHE && aLoadType != LOAD_ERROR_PAGE) {
+    if (shAvailable && mCurrentURI && !mOSHE && aLoadType != LOAD_ERROR_PAGE) {
         NS_ASSERTION(IsAboutBlank(mCurrentURI), "no SHEntry for a non-transient viewer?");
     }
 #endif