Adding critical check for null.

removing unneded assignment to temp var.

xpinstall/src/nsInstallFolder.cpp

@@ -116,6 +116,8 @@ nsInstallFolder::nsInstallFolder(const nsString& aFolderID, const nsString& aRel
         // if it already exists...
         nsCOMPtr<nsILocalFile> dirCheck;
         NS_NewLocalFile(aFolderID.ToNewCString(), getter_AddRefs(dirCheck));
+        if (dirCheck)
+        {
             dirCheck->IsDirectory(&flagIsDir);
             dirCheck->Exists(&flagExists);
             if ( flagIsDir || !flagExists )
@@ -139,7 +141,7 @@ nsInstallFolder::nsInstallFolder(const nsString& aFolderID, const nsString& aRel
             }
         }
     }
-
+}
 
 nsInstallFolder::nsInstallFolder(nsInstallFolder& inFolder, const nsString& subString)
 {
@@ -291,17 +293,7 @@ nsInstallFolder::SetDirectoryPath(const nsString& aFolderID, const nsString& aRe
 
             case 109: ///////////////////////////////////////////////////////////  File URL
                 {
-                    if (aRelativePath.IsEmpty())
-                    {
-                        mFileSpec = nsnull;
-                        return;
-                    }
-                    
                     nsCOMPtr<nsILocalFile> temp;
-
-                    nsString tempFileURLString = aFolderID;
-                    tempFileURLString += aRelativePath;
-
                     NS_NewLocalFile(aRelativePath.ToNewCString(), getter_AddRefs(temp));
                     mFileSpec = temp;