Disable extensions to avoid logging loading error

LOOT doesn't bundle the extensions resources, because it doesn't use
extensions, but this has resulted in errors being logged that aren't
actually a problem.

src/gui/loot_app.cpp

@@ -58,6 +58,7 @@ namespace loot {
 
             // Disable spell checking.
             command_line->AppendSwitch("--disable-spell-checking");
+            command_line->AppendSwitch("--disable-extensions");
         }
     }