fix(L3): isUnlocked() returns false when no accounts exposed

_metamask.isUnlocked() now checks provider.selectedAddress instead of
always returning true.

src/content/inpage.js

@@ -134,7 +134,7 @@
         // Some dApps (wagmi) check this to confirm MetaMask-like behavior
         _metamask: {
             isUnlocked() {
-                return Promise.resolve(true);
+                return Promise.resolve(provider.selectedAddress !== null);
             },
         },
     };